JP5908223B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device and a driving method thereof.

Liquid crystal display devices are roughly classified into two types, a transmission type and a reflection type.

A transmissive liquid crystal display device uses a backlight such as a cold cathode fluorescent lamp and utilizes the optical modulation action of the liquid crystal so that light from the backlight is transmitted through the liquid crystal and output to the outside of the liquid crystal display device. In this case, a state in which no image is output is selected, bright and dark are displayed, and an image is displayed by combining them.

In addition, the reflective liquid crystal display device utilizes the optical modulation action of the liquid crystal, and the external light, that is, the incident light is reflected by the pixel electrode and output to the outside of the device, and the incident light is not output to the outside of the device. An image is displayed by selecting a state, displaying bright and dark, and combining them.

As a display method of the liquid crystal display device, a color filter method and a field sequential method are known. A liquid crystal display device that performs display by a field sequential method is provided with a plurality of light sources (for example, R (red), G (green), and B (blue)) that exhibit different colors. A plurality of light sources exhibiting different colors emit light sequentially, and a desired color is formed by controlling transmission of light exhibiting each color for each pixel, and color display is performed. That is, the field sequential method is a method in which a desired color is formed by time division for each light exhibiting a specific color.

  Patent Document 1 discloses a liquid crystal display device that performs display by a field sequential method. Specifically, each pixel is provided with a transistor that controls input of an image signal, a signal holding capacitor that holds the image signal, and a transistor that controls movement of charges from the signal holding capacitor to the display pixel capacitor. A liquid crystal display device is disclosed. The liquid crystal display device having the above structure can perform writing of an image signal to the signal holding capacitor and display corresponding to the charge held in the display pixel capacitor in parallel.

JP 2009-42405 A

An object of the present invention is to provide a liquid crystal display device capable of recognizing an image display according to the environment in a bright or dim environment around the liquid crystal display device.

Another object is to provide a liquid crystal display device that can display an image in both a reflection mode using external light as an illumination light source and a transmission mode using a backlight.

Provide a display area (reflection area) that reflects light incident through the liquid crystal layer and a display area (transmission area) that transmits light from the backlight to switch between transmission mode and reflection mode A liquid crystal display device capable of performing the above. In the case of the reflection mode, the first transistor connected to the first pixel electrode in the reflection region is driven, and in the case of the transmission mode, the second transistor connected to the second pixel electrode in the transmission region. Drive. By operating these two transistors separately, the display area of the reflective area and the transmissive area can be controlled independently.

In addition, in the display of the transmissive region, the image signal writing and the backlight lighting are not sequentially performed on the entire pixel portion, but the image signal writing and the backlight lighting are sequentially performed for each specific region of the pixel portion. The field sequential method is used. As the light source of the backlight, a plurality of light emitting diodes (LEDs) that can reduce power consumption and adjust the intensity of light compared to cold cathode fluorescent lamps are used.

The new field-sequential method changes the display that is visible to the user from the display based on the original display information due to the lack of specific display information due to the blockage of the display for a short time such as the blink of the user. (Deterioration) (also referred to as color break or color breakup) can be reduced.

One embodiment of the present invention disclosed in this specification includes a backlight provided with a pixel portion and a panel provided with a driver circuit that controls input of an image signal to the pixel portion, and the backlight is different. A plurality of light sources that emit hue light. Then, the driving method of the light source is switched between when a full color image is displayed and when a monochrome image is displayed.

When displaying a full-color image, the pixel mode is divided into a plurality of regions using a new field sequential method, and lighting of the light source is controlled for each region. Specifically, the pixel portion has at least a first region and a second region, and a plurality of lights having different hues are sequentially supplied to the first region according to a first rotation number, The plurality of lights having different hues in the second region are sequentially supplied in accordance with a second rotation number different from the first rotation number.

When displaying a monochrome image, stop the light supply from the light source to enter the reflection mode, and use the external light to display a still image or a moving image for the entire reflection area of the pixel unit or for each area. Do.

Furthermore, in one embodiment of the present invention, when the monochrome image is a still image, the driving frequency is set lower than when the monochrome image is a moving image. In one embodiment of the present invention, in order to reduce the driving frequency, the pixel portion of the liquid crystal display device is provided with an insulating film with extremely low off-state current for controlling the liquid crystal element and holding of the voltage applied to the liquid crystal element. A gate field effect transistor (hereinafter simply referred to as a transistor) is provided. By using a transistor with extremely low off-state current, a period during which a voltage applied to the liquid crystal element is held can be extended. Therefore, when an image signal having the same image information is written in the pixel portion over several consecutive frame periods like a still image, even if the drive frequency is lowered, in other words, within a certain period. Even if the number of times of writing the image signal is reduced, the display of the image can be maintained.

The transistor includes a channel formation region containing a semiconductor material having a wider band gap than a silicon semiconductor and a lower intrinsic carrier density than a silicon semiconductor. By including the semiconductor material having the above characteristics in the channel formation region, a transistor with extremely low off-state current can be realized. As such a semiconductor material, for example, an oxide semiconductor having a large band gap about three times that of silicon can be given. By using the transistor having the above structure as a switching element for holding a voltage applied to the liquid crystal element, the liquid crystal element can be compared with a case where a transistor formed of a semiconductor material such as normal silicon or germanium is used. It is possible to prevent the leakage of charges.

The pixel portion includes a region in which the transmittance of the liquid crystal layer is controlled according to the voltage of the input full-color image signal, a first transistor that controls holding of the voltage in the liquid crystal layer that overlaps the region, and an input monochrome image A region in which the reflectance of the liquid crystal layer is controlled in accordance with the voltage of the image signal and a second transistor that controls holding of the voltage in the liquid crystal layer overlapping the region are included. The first and second transistors include a semiconductor material whose band gap is wider than that of the silicon semiconductor and whose intrinsic carrier density is lower than that of the silicon semiconductor, such as an oxide semiconductor, in the channel formation region.

Note that an oxide semiconductor (purified OS) in which oxygen vacancies are reduced by addition of oxygen after impurities such as water or hydrogen serving as an electron donor (donor) are reduced is i-type (intrinsic semiconductor) or i-type Infinitely close. Therefore, a transistor including the above oxide semiconductor has a characteristic of extremely low off-state current. Specifically, an oxide semiconductor has a hydrogen concentration measured by secondary ion mass spectrometry (SIMS) of 5 × 10 ¹⁹ / cm ³ or less, preferably 5 × 10 ¹⁸ / cm ³ or less. More preferably, it is 5 × 10 ¹⁷ / cm ³ or less, and further preferably 1 × 10 ¹⁶ / cm ³ or less. The carrier density of the oxide semiconductor film that can be measured by Hall effect measurement is less than 1 × 10 ¹⁴ / cm ³ , preferably less than 1 × 10 ¹² / cm ³ , and more preferably less than 1 × 10 ¹¹ / cm ³ . . The band gap of the oxide semiconductor is 2 eV or more, preferably 2.5 eV or more, more preferably 3 eV or more. By using an oxide semiconductor film in which the concentration of impurities such as moisture or hydrogen is sufficiently reduced and oxygen vacancies are reduced, the off-state current of the transistor can be reduced.

Here, the analysis of the hydrogen concentration in the oxide semiconductor film is mentioned. Measurement of hydrogen concentration in the oxide semiconductor film and the conductive film is performed by secondary ion mass spectrometry (SIMS). In SIMS analysis, it is known that, based on the principle, it is difficult to accurately obtain data in the vicinity of the sample surface and in the vicinity of the laminated interface with films of different materials. Therefore, when analyzing the distribution in the thickness direction of the hydrogen concentration in the film by SIMS, the average value in a region where there is no extreme variation in the value and an almost constant value is obtained in the range where the target film exists. Adopted as hydrogen concentration. Further, when the thickness of the film to be measured is small, there may be a case where an area where a substantially constant value is obtained cannot be found due to the influence of the hydrogen concentration in the adjacent film. In this case, the maximum value or the minimum value of the hydrogen concentration in the region where the film exists is adopted as the hydrogen concentration in the film. Further, in the region where the film is present, when there is no peak peak having the maximum value and no valley peak having the minimum value, the value of the inflection point is adopted as the hydrogen concentration.

Specifically, it can be proved by various experiments that the off-state current of a transistor using an oxide semiconductor film in which an impurity such as moisture or hydrogen is reduced and oxygen vacancies are reduced by addition of oxygen as an active layer is low. . For example, even in an element having a channel width of 1 × 10 ⁶ μm and a channel length of 10 μm, when the voltage between the source electrode and the drain electrode (drain voltage) is in the range of 1 V to 10 V, the off-current (gate electrode and source electrode) The drain current when the voltage between them is 0 V or less) can be obtained below the measurement limit of the semiconductor parameter analyzer, that is, 1 × 10 ⁻¹³ A or less. In this case, it can be seen that the off-current density corresponding to a value obtained by dividing the off-current by the channel width of the transistor is 100 zA / μm or less. Further, off-state current density was measured using a circuit in which a capacitor and a transistor are connected and charge flowing into or out of the capacitor is controlled by the transistor. In this measurement, an off-state current density of the transistor was measured from the change in the amount of charge per unit time of the capacitor using an oxide semiconductor film in the channel formation region of the transistor. As a result, it was found that when the voltage between the source electrode and the drain electrode of the transistor is 3 V, an even lower off-current density of several tens of yA / μm can be obtained. Therefore, in the semiconductor device according to one embodiment of the present invention, the off-state current density of the transistor including an oxide semiconductor film as an active layer is 100 yA / μm or less, preferably 10 yA / μm, depending on the voltage between the source electrode and the drain electrode. It can be set to μm or less, more preferably 1 yA / μm or less. Therefore, a transistor using an oxide semiconductor film as an active layer has a significantly lower off-state current than a transistor using silicon having crystallinity.

Note that as oxide semiconductors, indium oxide, tin oxide, zinc oxide, binary metal oxides such as In—Zn oxides, Sn—Zn oxides, Al—Zn oxides, Zn—Mg oxides are used. Oxides, Sn—Mg oxides, In—Mg oxides, In—Ga oxides, In—Ga—Zn oxides (also referred to as IGZO) which are oxides of ternary metals, In— Al-Zn oxide, In-Sn-Zn oxide, Sn-Ga-Zn oxide, Al-Ga-Zn oxide, Sn-Al-Zn oxide, In-Hf-Zn oxide In-La-Zn-based oxide, In-Ce-Zn-based oxide, In-Pr-Zn-based oxide, In-Nd-Zn-based oxide, In-Sm-Zn-based oxide, In-Eu -Zn oxide, In-Gd-Zn oxide, In-Tb-Zn oxide, I -Dy-Zn oxide, In-Ho-Zn oxide, In-Er-Zn oxide, In-Tm-Zn oxide, In-Yb-Zn oxide, In-Lu-Zn oxide Oxides, In-Sn-Ga-Zn-based oxides that are quaternary metal oxides, In-Hf-Ga-Zn-based oxides, In-Al-Ga-Zn-based oxides, In-Sn-Al A —Zn-based oxide, an In—Sn—Hf—Zn-based oxide, or an In—Hf—Al—Zn-based oxide can be used.

Note that, for example, an In—Ga—Zn-based oxide means an oxide containing In, Ga, and Zn, and there is no limitation on the ratio of In, Ga, and Zn. Moreover, metal elements other than In, Ga, and Zn may be contained.

Alternatively, a material represented by InMO ₃ (ZnO) _m (m> 0 is satisfied, and m is not an integer) may be used as the oxide semiconductor. Note that M represents one metal element or a plurality of metal elements selected from Ga, Fe, Mn, and Co. Alternatively, a material represented by In ₂ SnO ₅ (ZnO) _n (n> 0 is satisfied, and n is an integer) may be used as the oxide semiconductor.

A liquid crystal display that enables image display in both the reflective mode using external light as the illumination light source and the transmissive mode using the backlight, depending on the environment, whether the surroundings of the liquid crystal display device are bright or dim. A device can be realized. For example, when displaying a moving image, the transmission mode is set, and when displaying a still image, the reflection mode is set.

Using a transistor with extremely low off-state current, the period during which the voltage applied to the liquid crystal element is held can be extended. For example, the driving frequency when displaying a still image is higher than the driving frequency when displaying a moving image Can be lowered. Therefore, a liquid crystal display device with reduced power consumption in displaying a still image can be realized.

1 is a block diagram illustrating a configuration of a liquid crystal display device. The figure which shows the structure of a panel and a pixel. The figure which showed typically the operation | movement of a liquid crystal display device and a backlight. The figure which shows typically an example of the hue of the light supplied to each area | region. The figure which shows typically an example of extinction of the light supplied to each area | region. FIG. 9 illustrates a structure of a scan line driver circuit. The figure which showed typically the xth pulse output circuit 20_x. The figure which shows the structure of a pulse output circuit, and its timing chart. FIG. 9 is a timing chart of a scan line driver circuit. FIG. 9 is a timing chart of a scan line driver circuit. FIG. 9 illustrates a structure of a signal line driver circuit. The figure which shows an example of the timing of the image signal (DATA) supplied to a signal line. The figure which shows the timing of the scanning of a selection signal, and the timing of lighting of a backlight. The figure which shows the timing of the scanning of a selection signal, and the timing of light extinction of a backlight. The figure which shows the structure of a panel. FIG. 9 illustrates a structure of a scan line driver circuit. FIG. 9 is a timing chart of a scan line driver circuit. FIG. 9 illustrates a structure of a signal line driver circuit. The figure which shows the structure of a pulse output circuit. The figure which shows the structure of a pulse output circuit. 10 is a cross-sectional view illustrating a method for manufacturing a transistor. FIG. FIG. 14 is a cross-sectional view of a transistor. Sectional drawing which shows the manufacturing method of a liquid crystal display device. An example of a top view of a pixel. A cross-sectional view of a pixel. The top view and sectional drawing of a liquid crystal display device. 4A and 4B are a top view and a cross-sectional view illustrating a structure of a liquid crystal display device. Illustration of electronic equipment. 3A and 3B illustrate a structure of a transistor. The figure which shows the definition of Vth. The figure which shows a light negative bias test result.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the present invention is not limited to the following description, and it will be easily understood by those skilled in the art that modes and details can be variously changed. In addition, the present invention is not construed as being limited to the description of the embodiments below.

(Embodiment 1)
In this embodiment, a liquid crystal display device having a still image mode and a moving image mode will be described with reference to FIG. In this specification, an operation performed when the display device determines that an image signal input to the display device is a still image is referred to as a still image mode, and an operation performed when the display device is determined as a moving image is referred to as a moving image mode.

The liquid crystal display device 400 of this embodiment includes a plurality of image memories 401, an image data selection circuit 402, a selector 403, a CPU 404, a controller 405, a panel 406, a backlight 407, and a backlight control circuit 408. And have.

In the plurality of image memories 401, image data (full color image data 410) corresponding to the full color image input to the liquid crystal display device 400 is stored. The full color image data 410 includes image data corresponding to a plurality of hues. Each of the plurality of image memories 401 stores image data corresponding to each hue.

As the image memory 401, for example, a storage circuit such as a DRAM (Dynamic Random Access Memory) or SRAM (Static Random Access Memory) can be used.

The image data selection circuit 402 reads full color image data corresponding to each hue stored in the plurality of image memories 401 in accordance with an instruction from the controller 405 and sends the read data to the selector 403.

The liquid crystal display device 400 also receives image data (monochrome image data 411) corresponding to a monochrome image. The input monochrome image data 411 is input to the selector 403.

Note that a plurality of light sources exhibiting colors of different hues are used, and an image displayed with gradation of each color is a full color image. Further, the light source is turned off, and the image displayed by the reflective electrode is a monochrome image.

In this embodiment, the monochrome image data 411 is directly input to the selector 403. However, the present invention is not limited to this configuration. Similarly to the full-color image data 410, the monochrome image data 411 may be temporarily stored in the image memory 401 and read out by the image data selection circuit 402. In this case, the selector 403 is included in the image data selection circuit 402.

Further, the monochrome image data 411 may be created by combining the full color image data 410 in the liquid crystal display device 400.

The CPU 404 performs control so that the operations of the selector 403 and the controller 405 are switched between when a full color image is displayed and when a monochrome image is displayed.

Specifically, when displaying a full-color image, the selector 403 selects the input full-color image data 410 according to a command from the CPU 404 and supplies it to the panel 406. Further, the controller 405 supplies a drive signal synchronized with the full-color image data 410 or a power supply potential used when displaying a full-color image to the panel 406 in accordance with a command from the CPU 404.

Alternatively, when displaying a monochrome image, the selector 403 selects the input monochrome image data 411 in accordance with a command from the CPU 404 and supplies the selected monochrome image data 411 to the panel 406. In addition, the controller 405 supplies a drive signal synchronized with the monochrome image data 411 or a power supply potential used when displaying a monochrome image to the panel 406 in accordance with a command from the CPU 404.

The panel 406 includes a pixel portion 412 having a liquid crystal element in each pixel, a first scan line driver circuit 414a, a first signal line driver circuit 413a, a second scan line driver circuit 414b, and a second signal line driver circuit. And a driving circuit such as 413b. Full color image data 410 or monochrome image data 411 from the selector 403 is supplied to the first signal line driver circuit 413a or the second signal line driver circuit 413b. In addition, a driving signal or a power supply potential from the controller 405 is supplied to the first scan line driver circuit 414a, the first signal line driver circuit 413a, the second scan line driver circuit 414b, or the second signal line driver circuit 413b. Given.

Note that the drive signal includes a signal line driver circuit start pulse signal (SSP1, SSP2) for controlling the operation of the first signal line driver circuit 413a or the second signal line driver circuit 413b, and a signal line driver circuit clock signal. (SCK1, SCK2), a scanning line driving circuit start pulse signal (GSP) for controlling the operation of the first scanning line driving circuit 414a or the second scanning line driving circuit 414b, and a scanning line driving circuit clock signal (GCK). Etc. are included.

The backlight 407 is provided with a plurality of light sources that emit light having different hues. The controller 405 controls driving of the light source included in the backlight 407 via the backlight control circuit 408.

Note that switching between full-color image display and monochrome image display can be performed artificially. In this case, the input device 420 may be provided in the liquid crystal display device 400, and the CPU 404 may control the switching according to a signal from the input device 420. For example, the user controls switching between the display of a full-color image and the display of a monochrome image by using a switch or the like provided in the liquid crystal display device 400.

In addition, the liquid crystal display device 400 exemplified in this embodiment may include a photometric circuit 421. The photometry circuit 421 is a circuit that measures the brightness of the environment where the liquid crystal display device 400 is used. Then, the CPU 404 may control switching between full-color image display and monochrome image display according to the brightness detected by the photometry circuit 421.

For example, when the liquid crystal display device 400 exemplified in this embodiment is used in a dim environment, the CPU 404 selects display of a full-color image according to a signal from the photometry circuit 421 and uses it in a bright environment. The CPU 404 may select display of a monochrome image in accordance with a signal from. Note that a threshold value may be set in advance in the photometric circuit 421 so that the backlight is turned on when the brightness of the usage environment falls below the threshold value.

Next, a specific structure of the panel of the liquid crystal display device according to one embodiment of the present invention is described with an example.

FIG. 2A illustrates a configuration example of a liquid crystal display device. The liquid crystal display device illustrated in FIG. 2A includes a pixel portion 10, a first scan line driver circuit 11a, a second scan line driver circuit 11b, a first signal line driver circuit 12a, and a second And a signal line driver circuit 12b. In one embodiment of the present invention, the pixel portion 10 is divided into a plurality of regions. Specifically, FIG. 2A illustrates a case where the pixel portion 10 is divided into three regions (regions 101 to 103). Each region has a plurality of pixels 15 arranged in a matrix.

Further, the pixel portion 10 includes m scanning lines GLa whose potential is controlled by the first scanning line driving circuit 11a and n signal lines SLa whose potential is controlled by the first signal line driving circuit 12a. And are provided. The m scanning lines GLa are divided into a plurality of groups according to the number of regions of the pixel unit 10. For example, in the case of FIG. 2A, since the pixel portion 10 is divided into three regions, the m scanning lines GLa are also divided into three groups. The scanning lines GLa belonging to each group are connected to the plurality of pixels 15 included in the region corresponding to the group. Specifically, each scanning line GLa is connected to n pixels 15 arranged in any row among a plurality of pixels 15 arranged in a matrix in each region.

In addition, each signal line SLa is connected to m pixels 15 arranged in any column among the plurality of pixels 15 arranged in m rows and n columns in the pixel unit 10 regardless of the region. Is done.

FIG. 2B is a diagram illustrating an example of a circuit diagram of the pixel 15 included in the liquid crystal display device illustrated in FIG.

The pixel 15 is roughly divided into a transmission region where the pixel electrode transmits light and a reflection region where the reflection electrode reflects light incident through the liquid crystal layer. The transmissive region includes a first pixel transistor 16a, a first liquid crystal element 18a, and a first capacitor element 17a. The first pixel transistor 16a has a gate connected to the first scanning line GLa, a first terminal serving as one of the source and drain connected to the first signal line SLa, and a second terminal serving as the other of the source and drain. Are connected to one electrode of the first liquid crystal element 18a and the first electrode of the first capacitor element 17a. The other electrode of the first liquid crystal element 18a is connected to the common electrode. Note that the second electrode of the first capacitor 17a is connected to a capacitor line.

Further, the reflection region includes a second pixel transistor 16b, a second liquid crystal element 18b, and a second capacitor element 17b. The second pixel transistor 16b has a gate connected to the second scanning line GLb, a first terminal serving as one of the source and drain connected to the second signal line SLb, and a second terminal serving as the other of the source and drain. Is connected to one electrode of the second liquid crystal element 18b and the first electrode of the second capacitor element 17b. Note that the other electrode of the second liquid crystal element 18b is connected to the common electrode. Note that the second electrode of the second capacitor 17b is connected to a capacitor line.

In FIG. 2, the first scanning line GLa and the second scanning line GLb are separately driven by the first scanning line driving circuit 11a and the second scanning line driving circuit 11b. The first signal line SLa and the second signal line SLb are supplied with different image signals by the first signal line driver circuit 12a and the second signal line driver circuit 12b. In the first liquid crystal element 18a in the transmissive region and the second liquid crystal element 18b in the reflective region, gradation control based on different image signals is performed.

Note that the first pixel transistor 16a and the second pixel transistor 16b are preferably formed using a transistor including an oxide semiconductor layer. By using a transistor with an extremely small off-state current as the second pixel transistor 16b, a long period during which the voltage supplied to the second liquid crystal element 18b is held can be secured. Therefore, when an image signal having the same image information is written in the pixel unit 10 over several consecutive frame periods like a still image, the drive frequency is lowered, in other words, pixels within a certain period. The image display can be maintained even if the number of times of writing the image signal to the unit 10 is reduced. For example, a transistor using an oxide semiconductor film with high purity and reduced oxygen vacancies as an active layer as described above is used for the second pixel transistor 16b, so that the writing interval of image signals is 10. Seconds or longer, preferably 30 seconds or longer, more preferably 1 minute or longer. The longer the interval at which the image signal is written, the more the power consumption can be reduced.

Further, when visually recognizing an image obtained by writing an image signal a plurality of times, the human eye visually recognizes an image that is switched a plurality of times. Therefore, it may appear as fatigue in human eyes. As described in the present embodiment, the configuration of reducing the number of times of writing image signals has an effect of reducing eye fatigue.

In addition, since the potential of the image signal can be held for a longer period, the second liquid crystal element 18b is not connected to the second capacitor element 17b in order to hold the potential of the image signal. It is possible to prevent the displayed image quality from deteriorating.

The first pixel transistor 16a and the second pixel transistor 16b are not limited to transistors having an oxide semiconductor layer as long as the band gap is wider than that of a silicon semiconductor and the intrinsic carrier density is lower than that of a silicon semiconductor. A transistor including a compound semiconductor such as silicon carbide (SiC) or gallium nitride (GaN) may be used.

Each of the first liquid crystal element 18a and the second liquid crystal element 18b includes a pixel electrode, a counter electrode, and a liquid crystal layer including a liquid crystal to which a voltage between the pixel electrode and the counter electrode is applied. Yes.

Examples of liquid crystal materials used for the liquid crystal layer include nematic liquid crystal, cholesteric liquid crystal, smectic liquid crystal, discotic liquid crystal, thermotropic liquid crystal, lyotropic liquid crystal, low molecular liquid crystal, polymer dispersed liquid crystal (PDLC), ferroelectric liquid crystal, Ferroelectric liquid crystal, main chain type liquid crystal, side chain type polymer liquid crystal, banana type liquid crystal and the like can be mentioned.

Alternatively, a liquid crystal exhibiting a blue phase for which an alignment film is unnecessary may be used. The blue phase is one of the liquid crystal phases. When the temperature of the cholesteric liquid crystal is increased, the blue phase appears immediately before the transition from the cholesteric phase to the isotropic phase. Since the blue phase appears only in a narrow temperature range, the temperature range is improved by adding a chiral agent or an ultraviolet curable resin. A liquid crystal composition containing a liquid crystal exhibiting a blue phase and a chiral agent has a response speed of 10 μsec. 100 μsec. Since it is short as follows and is optically isotropic, alignment treatment is unnecessary, and the viewing angle dependency is small, which is preferable.

In addition, as a driving method of the liquid crystal, a TN (Twisted Nematic) mode, an STN (Super Twisted Nematic) mode, a VA (Vertical Alignment) mode, an MVA (Multi-domain Vertical Alignment) mode, an IPS (In-P) mode, an IPS (In-P) mode (Optically Compensated Birefringence) mode, ECB (Electrically Controlled Birefringence) mode, FLC (Ferroelectric Liquid Crystal Liquid) mode, AFLC (Anti-Ferroelectric LCLiquid Liquid Liquid mode) er Dispersed Liquid Crystal) mode, PNLC (Polymer Network Liquid Crystal) mode, it is possible to apply such a guest-host mode.

The pixel 15 may further include other circuit elements such as a transistor, a diode, a resistance element, a capacitor element, and an inductance as necessary.

Further, by performing inversion driving in which the polarity of the potential of the image signal is inverted with respect to the potential of the counter electrode, deterioration of the liquid crystal called burn-in can be prevented. However, when inversion driving is performed, the potential change applied to the signal line when the polarity of the image signal changes increases, and thus the potential difference between the source electrode and the drain electrode of the second pixel transistor 16b increases. Therefore, the second pixel transistor 16b is likely to be deteriorated in characteristics such as a threshold voltage shift. Further, in order to maintain the voltage held in the second liquid crystal element 18b, the off-state current is required to be low even if the potential difference between the source electrode and the drain electrode is large. In this embodiment, a semiconductor such as an oxide semiconductor is used for the second pixel transistor 16b. Therefore, the withstand voltage of the second pixel transistor 16b can be increased and the off-state current can be significantly reduced. Therefore, as compared with the case where a transistor formed using a semiconductor material such as silicon or germanium is used, deterioration of the second pixel transistor 16b can be prevented and the voltage held in the second liquid crystal element 18b can be maintained. it can.

Next, an example of the operation of the panel will be described together with the operation of the backlight. FIG. 3 is a diagram schematically showing the operation of the liquid crystal display device and the backlight. As shown in FIG. 3, the operation of the liquid crystal display device according to one embodiment of the present invention includes a period for displaying a full-color image (full-color image display period 301) and a period for displaying a moving image of a monochrome image (a monochrome moving-image display period 302). ) And a period during which a monochrome image is displayed (monochrome still image display period 303).

In the full-color image display period 301, one frame period is composed of a plurality of subframe periods. An image signal is written to the pixel portion every subframe period. A driving signal is continuously supplied to a driving circuit such as a scanning line driving circuit or a signal line driving circuit while displaying an image. Therefore, in the full-color image display period 301, the driving circuit is in an operating state. In the full-color image display period 301, the hue of light supplied to the pixel portion by the backlight is switched every subframe period. Then, an image signal corresponding to each hue is sequentially written in the pixel portion, and one image is formed by writing image signals corresponding to all the hues within one frame period. Therefore, in the full-color image display period 301, the number of times of writing image signals to the pixel portion in one frame period is plural, and the number is determined by the number of hues of light supplied from the backlight.

In the monochrome moving image display period 302, as in the full color image display period 301, the image signal is written to the pixel portion every frame period. A driving signal is continuously supplied to a driving circuit such as a scanning line driving circuit or a signal line driving circuit while displaying an image. Therefore, in the monochrome moving image display period 302, the driving circuit is in an operating state. In the monochrome moving image display period 302, the hue of light supplied to the pixel portion by the backlight is not switched every frame period, and light of one hue is continuously supplied to the pixel portion. Then, one image is formed by sequentially writing image signals corresponding to the one hue into the pixel portion within one frame period. Therefore, in the monochrome moving image display period 302, the number of times of writing the image signal to the pixel portion in one frame period is one.

In the monochrome still image display period 303, as in the full-color image display period 301, the image signal is written to the pixel portion every frame period. However, unlike the full-color image display period 301 and the monochrome moving image display period 302, a drive signal is supplied to the drive circuit when the image signal is written to the pixel portion, and the drive signal is supplied to the drive circuit after the writing is completed. Stop. Therefore, in the monochrome still image display period 303, the driving circuit is in a non-operating state except when an image signal is written. In the monochrome still image display period 303, the backlight is turned off. Then, one image is formed by sequentially writing image signals to the pixel portion within one frame period. Therefore, in the monochrome still image display period 303, the number of times of writing the image signal to the pixel portion in one frame period is one.

In the monochrome moving image display period 302, it is desirable to provide 60 frame periods or more per second in order to prevent flickering of images such as flicker from being visually recognized. In the monochrome still image display period 303, one frame period can be extremely long, for example, 1 minute or longer. By lengthening one frame period, the period during which the driver circuit is not operating can be lengthened, so that power consumption of the liquid crystal display device can be reduced.

In addition, the liquid crystal display device according to one embodiment of the present invention does not need to use a color filter. Therefore, the cost can be reduced as compared with a liquid crystal display device using a color filter.

Note that in the full-color image display period 301, a plurality of lights having different hues are sequentially supplied to each region of the pixel portion in one frame period. FIG. 4 schematically shows an example of the hue of light supplied to each region. FIG. 4 illustrates the case where the pixel portion is divided into three regions as illustrated in FIG. Further, FIG. 4 illustrates a case where red (R) light, blue (B) light, and green (G) light is supplied to the pixel portion from the backlight.

First, in FIG. 4A, red (R) light is supplied to the region 101, green (G) light is supplied to the region 102, and blue (B) light is supplied to the region 103 in the first subframe period. It shows how it is. 4B, green (G) light is supplied to the region 101, blue (B) light is supplied to the region 102, and red (R) light is supplied to the region 103 in the next subframe period. It shows how it is. 4C, blue (B) light is supplied to the region 101, red (R) light is supplied to the region 102, and green (G) light is supplied to the region 103 in the next subframe period. It shows how it is done.

Then, when all the subframe periods are finished, one frame period is finished. In one frame period, a full color image can be displayed as the hue of light supplied to each region makes a round. Focusing on each region, in the region 101, the hue of the supplied light changes in the order of red (R), green (G), and blue (B). In the region 102, the hue of the supplied light changes in the order of green (G), blue (B), and red (R). In the region 103, the hue of the supplied light changes in the order of blue (B), red (R), and green (G). Therefore, it can be seen that a plurality of lights having different hues are sequentially supplied to each region according to different rotation numbers.

Note that FIG. 4 illustrates an example in which only light of one hue is supplied to one region in each subframe period; however, one embodiment of the present invention is not limited to this structure. For example, in each region, the hue of the light supplied in order from the portion where the writing of the image signal is completed may be switched. In this case, the irradiation region to which the light of each hue is supplied does not necessarily match the region formed by dividing the pixel portion.

Further, in the monochrome moving image display period 302 and the monochrome still image display period 303, all of the plurality of lights having different hues are turned off. FIG. 5 schematically shows an example of turning off the light in each region. Note that FIG. 5 shows an example in which the pixel portion is divided into three regions as shown in FIG. As shown in FIG. 5, the backlights are all turned off in the areas 101, 102, and 103.

<Configuration Example of First Scan Line Driver Circuit 11a> FIG. 6 is a diagram showing a configuration example of the first scan line driver circuit 11a shown in FIG. The first scan line driver circuit 11a illustrated in FIG. 6 includes a first pulse output circuit 20_1 to an mth pulse output circuit 20_m. The selection signals output from the first pulse output circuit 20_1 to the m-th pulse output circuit 20_m are supplied to the m first scan lines GLa (scan lines GLa1 to GLam), respectively.

The first scan line driver circuit 11a includes a first scan line driver circuit first clock signal (GCK1) to a first scan line driver circuit fourth clock signal (GCK4), and a first pulse. The width control signal (PWC1) to the sixth pulse width control signal (PWC6) and the scan line drive circuit start pulse signal (GSP) are supplied as drive signals.

Note that in FIG. 6, the first pulse output circuit 20_1 to the k-th pulse output circuit 20_k (k is a multiple of 4 less than m / 2) are arranged in the scan line GLa1 to the scan line GLak arranged in the region 101. The case where it is connected to is illustrated. 6 illustrates a case where the (k + 1) th pulse output circuit 20_k + 1 to the 2kth pulse output circuit 20_2k are connected to the scanning lines GLak + 1 to GLa2k arranged in the region 102. 6 illustrates a case where the 2k + 1th pulse output circuit 20_2k + 1 to the mth pulse output circuit 20_m are connected to the scan lines GLa2k + 1 to Glam arranged in the region 103.

The first pulse output circuit 20_1 to the m-th pulse output circuit 20_m start operation in accordance with the scan line driver circuit start pulse signal (GSP) input to the first pulse output circuit 20_1, and the pulses are sequentially shifted. Outputs a selection signal.

Circuits having the same structure can be used for the first pulse output circuit 20_1 to the m-th pulse output circuit 20_m. Specific connection relations of the first pulse output circuit 20_1 to the m-th pulse output circuit 20_m are described with reference to FIGS.

FIG. 7 is a diagram schematically illustrating the x-th pulse output circuit 20_x (x is a natural number equal to or less than m). Each of the first pulse output circuit 20_1 to the m-th pulse output circuit 20_m includes a terminal 21 to a terminal 27. The terminals 21 to 24 and the terminal 26 are input terminals, and the terminals 25 and 27 are output terminals.

First, the terminal 21 will be described. A terminal 21 of the first pulse output circuit 20_1 is connected to a wiring for supplying a first scan line driver circuit start pulse signal (GSP), and the second pulse output circuit 20_2 to the m-th pulse output circuit 20_m. The terminal 21 is connected to the terminal 27 of the preceding pulse output circuit.

Next, the terminal 22 will be described. The terminal 22 of the (4a-3) th pulse output circuit 20_ (4a-3) (a is a natural number of m / 4 or less) supplies the first clock signal (GCK1) for the first scanning line driving circuit. The terminal 22 of the (4a-2) th pulse output circuit 20_ (4a-2) is connected to the wiring and is connected to the wiring for supplying the first scanning line driving circuit second clock signal (GCK2). The terminal 22 of the pulse output circuit 20_ (4a-1) of (4a-1) is connected to the wiring that supplies the third clock signal (GCK3) for the first scanning line driving circuit, and the 4a pulse output circuit 20_4a. The terminal 22 is connected to a wiring for supplying a fourth clock signal (GCK4) for the first scanning line driving circuit.

Next, the terminal 23 will be described. The terminal 23 of the (4a-3) th pulse output circuit 20_ (4a-3) is connected to a wiring for supplying the second clock signal (GCK2) for the first scan line driver circuit, and the (4a-2) th The terminal 23 of the first pulse output circuit 20_ (4a-2) is connected to the wiring for supplying the third clock signal (GCK3) for the first scan line driver circuit, and the (4a-1) th pulse output circuit 20_ ( The terminal 23 of 4a-1) is connected to the wiring that supplies the fourth clock signal (GCK4) for the first scanning line driving circuit, and the terminal 23 of the 4a pulse output circuit 20_4a is the first scanning line driving. It is connected to a wiring for supplying the first clock signal for circuit (GCK1).

Next, the terminal 24 will be described. The terminal 24 of the (2b-1) th pulse output circuit 20_ (2b-1) (b is a natural number equal to or less than k / 2) is connected to a wiring for supplying the first pulse width control signal (PWC1). The terminal 24 of the 2b-th pulse output circuit 20_2b is connected to the wiring for supplying the fourth pulse width control signal (PWC4), and the (2c-1) -th pulse output circuit 20_ (2c-1) (c is (A natural number of (k / 2 + 1) to k) is connected to a wiring for supplying the second pulse width control signal (PWC2), and the terminal 24 of the 2c pulse output circuit 20_2c is connected to the fifth pulse. The terminal 24 of the (2d-1) th pulse output circuit 20_ (2d-1) (d is a natural number not less than (k + 1) and not more than m / 2) is connected to the wiring for supplying the width control signal (PWC5). The third pulse width control signal (PWC3) Is connected to the supply wiring, the pulse output circuit 20_2d terminal 24 of the first 2d is connected to a wiring for supplying a sixth pulse width control signal (PWC6).

Next, the terminal 25 will be described. A terminal 25 of the x-th pulse output circuit 20_x is connected to the scanning line GLx arranged in the x-th row.

Next, the terminal 26 will be described. A terminal 26 of the y-th pulse output circuit 20_y (y is a natural number equal to or less than m−1) is connected to a terminal 27 of the (y + 1) -th pulse output circuit 20_ (y + 1), and the m-th pulse output circuit 20_m The terminal 26 is connected to a wiring for supplying an m-th pulse output circuit stop signal (STP). The m-th pulse output circuit stop signal (STP) is a terminal of the (m + 1) th pulse output circuit 20_ (m + 1) when the (m + 1) th pulse output circuit 20_ (m + 1) is provided. This corresponds to the signal output from the terminal 27. Specifically, the mth pulse output circuit 20_m is obtained by actually providing the (m + 1) th pulse output circuit 20_ (m + 1) as a dummy circuit or directly inputting the signal from the outside. Can be supplied to.

The connection relation of the terminal 27 of each pulse output circuit has already been described. For this reason, the above description is incorporated herein.

<Configuration Example 1 of Pulse Output Circuit>
Next, FIG. 8A illustrates an example of a specific structure of the x-th pulse output circuit 20 — x illustrated in FIG. The pulse output circuit illustrated in FIG. 8A includes transistors 31 to 39.

The gate electrode of the transistor 31 is connected to the terminal 21. The transistor 31 has a first terminal connected to a node to which a high power supply potential (Vdd) is applied, and a second terminal connected to the gate electrode of the transistor 33 and the gate electrode of the transistor 38.

The gate electrode of the transistor 32 is connected to the gate electrode of the transistor 34 and the gate electrode of the transistor 39. The transistor 32 has a first terminal connected to a node to which a low power supply potential (Vss) is applied, and a second terminal connected to the gate electrode of the transistor 33 and the gate electrode of the transistor 38.

The transistor 33 has a first terminal connected to the terminal 22 and a second terminal connected to the terminal 27.

The transistor 34 has a first terminal connected to a node to which a low power supply potential (Vss) is applied, and a second terminal connected to the terminal 27.

The gate electrode of the transistor 35 is connected to the terminal 21. The transistor 35 has a first terminal connected to a node to which a low power supply potential (Vss) is applied, and a second terminal connected to the gate electrode of the transistor 34 and the gate electrode of the transistor 39.

The gate electrode of the transistor 36 is connected to the terminal 26. The transistor 36 has a first terminal connected to a node to which a high power supply potential (Vdd) is applied, and a second terminal connected to the gate electrode of the transistor 34 and the gate electrode of the transistor 39. Note that the first terminal of the transistor 36 is connected to a node to which a power supply potential (Vcc) that is higher than the low power supply potential (Vss) and lower than the high power supply potential (Vdd) is applied. It can also be configured.

The gate electrode of the transistor 37 is connected to the terminal 23. The transistor 37 has a first terminal connected to a node to which a high power supply potential (Vdd) is applied, and a second terminal connected to the gate electrode of the transistor 34 and the gate electrode of the transistor 39. Note that the first terminal of the transistor 37 may be connected to a node to which the power supply potential (Vcc) is applied.

The transistor 38 has a first terminal connected to the terminal 24 and a second terminal connected to the terminal 25.

The transistor 39 has a first terminal connected to a node to which a low power supply potential (Vss) is applied, and a second terminal connected to the terminal 25.

Next, FIG. 8B illustrates an example of a timing chart of the pulse output circuit illustrated in FIG. Note that a period t1 to a period t7 illustrated in FIG. 8B indicate periods of the same length. The period t1 to the period t7 are each 1/3 of the pulse width of the first scanning line driver circuit first clock signal (GCK1) to the first scanning line driver circuit fourth clock signal (GCK4). It corresponds to 1/2 of the pulse width of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

In the pulse output circuit illustrated in FIG. 8A, the potential input to the terminal 21 is high level and the potential input to the terminal 22, the terminal 23, the terminal 24, and the terminal 26 is low level in the periods t1 and t2. Therefore, a low level potential is output from the terminal 25 and a low level potential is output from the terminal 27.

Next, in a period t3, the potential input to the terminal 21 and the terminal 24 is at a high level, and the potential input to the terminal 22, the terminal 23, and the terminal 26 is at a low level; To output a low level potential.

Next, in the period t4, the potential input to the terminal 22 and the terminal 24 is at a high level, and the potential input to the terminal 21, the terminal 23, and the terminal 26 is at a low level. To output a high level potential.

Next, in the period t5 and the period t6, the potential input to the terminal 22 is at a high level, and the potentials input to the terminal 21, the terminal 23, the terminal 24, and the terminal 26 are at a low level; A high level potential is output from the terminal 27.

Next, in the period t7, the potential input to the terminal 23 and the terminal 26 is high level, and the potential input to the terminal 21, the terminal 22, and the terminal 24 is low level. 27 outputs a low-level potential.

Next, FIG. 8C illustrates another example of the timing chart of the pulse output circuit illustrated in FIG. Note that a period t1 to a period t7 illustrated in FIG. 8C each have the same length. The period t1 to the period t7 are each 1/3 of the pulse width of the first scanning line driver circuit first clock signal (GCK1) to the first scanning line driver circuit fourth clock signal (GCK4). It corresponds to 1/3 of the pulse width of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

In the pulse output circuit illustrated in FIG. 8A, the potential input to the terminal 21 is high level and the potential input to the terminal 22, the terminal 23, the terminal 24, and the terminal 26 is low level in the periods t1 to t3. Therefore, a low level potential is output from the terminal 25 and a low level potential is output from the terminal 27.

Next, in periods t4 to t6, the potential input to the terminal 22 and the terminal 24 is in a high level, and the potential input to the terminal 21, the terminal 23, and the terminal 26 is in a low level. And a high level potential is output from the terminal 27.

<Operation Example of First Scan Line Driver Circuit in Full Color Image Display Period 301> Next, the first scan line driver circuit 11a described with reference to FIGS. 6, 7, and 8A will be described as an example. The operation of the first scanning line driving circuit 11a in the full color image display period 301 shown in FIG. 3 will be described.

FIG. 9 shows an example of a timing chart of the first scanning line driving circuit 11a in the full-color image display period 301. FIG. 9 illustrates a case where the subframe period SF1, the subframe period SF2, and the subframe period SF3 are provided in one frame period. A timing chart of the subframe period SF1 is shown as a representative example in FIG. However, FIG. 9 illustrates the case of m = 3k.

In FIG. 9, the scanning lines GLa1 to GLak are connected to the pixels in the region 101, the scanning lines GLak + 1 to the scanning lines GLa2k are connected to the pixels in the region 102, and the scanning lines GLa2k + 1 to GLa3k are connected to the pixels in the region 103. The timing chart in the case of being connected to a pixel is illustrated.

The first clock signal (GCK1) for the first scan line driver circuit periodically repeats a high level potential (high power supply potential (Vdd)) and a low level potential (low power supply potential (Vss)). Is a 1/4 signal. The second clock signal (GCK2) for the first scan line driver circuit is a signal whose phase is delayed by a quarter period from the first clock signal (GCK1) for the first scan line driver circuit. The third clock signal (GCK3) for the scanning line driving circuit is a signal having a half cycle phase delayed from the first clock signal (GCK1) for the first scanning line driving circuit. The fourth clock signal (GCK4) for use is a signal that is delayed by 3/4 cycle phase from the first clock signal (GCK1) for the first scanning line driving circuit.

The first pulse width control signal (PWC1) periodically repeats a high level potential (high power supply potential (Vdd)) and a low level potential (low power supply potential (Vss)) with a duty ratio of 1/3. Signal. In addition, the second pulse width control signal (PWC2) is a signal delayed by 1/6 cycle phase from the first pulse width control signal (PWC1), and the third pulse width control signal (PWC3) 1 pulse width control signal (PWC1) is delayed by 1/3 cycle phase, and the fourth pulse width control signal (PWC4) is 1/2 cycle phase from the first pulse width control signal (PWC1). The fifth pulse width control signal (PWC5) is a signal with a 2/3 cycle phase delayed from the first pulse width control signal (PWC1), and the sixth pulse width control signal (PWC5) PWC6) is a signal whose phase is delayed by 5/6 period from the first pulse width control signal (PWC1).

In FIG. 9, the first scan line driver circuit first clock signal (GCK1) to the first scan line driver circuit fourth clock signal (GCK4) and the first pulse width control signal (PWC1) are used. ) To the sixth pulse width control signal (PWC6) have a pulse width ratio of 3: 2.

Each subframe period SF starts in accordance with the fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP). The scan line driver circuit start pulse signal (GSP) has the same pulse width as the first scan line driver circuit first clock signal (GCK1) to the first scan line driver circuit fourth clock signal (GCK4). It is. The fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP) and the rise of the potential of the pulse of the first scan line driver circuit first clock signal (GCK1) are synchronized. Yes. In addition, the fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP) starts from the rise of the potential of the pulse of the first pulse width control signal (PWC1). Appears at a timing delayed by 1/6 period of PWC1).

Then, the pulse output circuit illustrated in FIG. 8A operates according to the timing chart illustrated in FIG. Therefore, as shown in FIG. 9, a selection signal in which pulses are sequentially shifted is supplied to the scanning lines GLa1 to GLak corresponding to the region 101. In addition, the pulses of the selection signals supplied to the scanning lines GLa1 to GLak are shifted so that the phase is delayed for a period corresponding to three-half of the pulse width. Note that the pulse widths of the selection signals supplied to the scanning lines GLa1 to GLak are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

Similarly to the case of the region 101, the scanning lines GLak + 1 to the scanning lines GLa2k corresponding to the region 102 are supplied with selection signals obtained by sequentially shifting the pulses. In addition, the pulse of the selection signal applied to the scanning lines GLak + 1 to GLa2k is shifted so that the phase is delayed for a period corresponding to three-half of the pulse width. Note that the pulse widths of the selection signals supplied to the scanning lines GLak + 1 to GLa2k are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

Similarly to the case of the region 101, the scanning lines GLa2k + 1 to GLa3k corresponding to the region 103 are supplied with selection signals obtained by sequentially shifting the pulses. In addition, the pulses of the selection signals given to the scanning lines GLa2k + 1 to GLa3k are shifted so that the phase is delayed for a period corresponding to three-half of the pulse width. Note that the pulse widths of the selection signals supplied to the scanning lines GLa2k + 1 to GLa3k are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

The pulses of the selection signal applied to the scanning line GLa1, the scanning line GLak + 1, and the scanning line GLa2k + 1 are sequentially shifted so that the phase is delayed for a period corresponding to a half of the pulse width.

<Operation Example of Second Scan Line Driver Circuit in Monochrome Still Image Display Period 303>
Next, taking the second scanning line driving circuit 11b as an example, the operation of the second scanning line driving circuit 11b in the monochrome still image display period 303 shown in FIG. 3 will be described.

FIG. 10 shows an example of a timing chart of the second scanning line driving circuit 11 b in the monochrome still image display period 303. FIG. 10 illustrates a case where a writing period for writing an image signal to a pixel and a holding period for holding the image signal are provided in one frame period.

For the second scan line driver circuit first clock signal (GCK1) to the second scan line driver circuit fourth clock signal (GCK4), signals similar to those in FIG. 9 can be used.

The first pulse width control signal (PWC1) and the fourth pulse width control signal (PWC4) are periodically at a high level (high power supply potential (Vdd)) in the first third period of the writing period. And a low-level potential (low power supply potential (Vss)), a signal having a duty ratio of ½, and a signal having a low-level potential in other periods. The fourth pulse width control signal (PWC4) is a signal having a 1/2 cycle phase delayed from the first pulse width control signal (PWC1).

Further, the second pulse width control signal (PWC2) and the fifth pulse width control signal (PWC5) are periodically set to a high level potential (high power supply potential (Vdd) in the middle ３ period of the writing period. )) And a low-level potential (low power supply potential (Vss)), a signal having a duty ratio of ½, and a signal having a low-level potential in other periods. The fifth pulse width control signal (PWC5) is a signal having a 1/2 cycle phase delayed from the second pulse width control signal (PWC2).

Further, the third pulse width control signal (PWC3) and the sixth pulse width control signal (PWC6) are periodically set to a high level potential (high power supply potential (Vdd) in the last one third period of the writing period. )) And a low-level potential (low power supply potential (Vss)), a signal having a duty ratio of ½, and a signal having a low-level potential in other periods. The sixth pulse width control signal (PWC6) is a signal having a half cycle phase delayed from the third pulse width control signal (PWC3).

In FIG. 10, the pulse widths of the second scan line driver circuit first clock signal (GCK1) to the second scan line driver circuit fourth clock signal (GCK4) and the first pulse width control signal (PWC1). ) To the sixth pulse width control signal (PWC6) have a pulse width ratio of 1: 1.

The frame period F starts in accordance with the fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP). The pulse width of the scan line driver circuit start pulse signal (GSP) is approximately the same as the second scan line driver circuit first clock signal (GCK1) to the second scan line driver circuit fourth clock signal (GCK4). It is. The fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP) and the rise of the potential of the pulse of the second scan line driver circuit first clock signal (GCK1) are synchronized. Yes. Further, the fall of the potential of the pulse of the scan line driver circuit start pulse signal (GSP) is synchronized with the rise of the potential of the pulse of the first pulse width control signal (PWC1).

With the above signal, the pulse output circuit illustrated in FIG. 8A operates according to the timing chart illustrated in FIG. Therefore, as shown in FIG. 10, a selection signal obtained by sequentially shifting pulses is supplied to the scanning lines GLb1 to GLbk corresponding to the region 101. In addition, the pulses of the selection signals supplied to the scanning lines GLb1 to GLbk are shifted so that the phase is delayed for a period corresponding to the pulse width. Note that the pulse widths of the selection signals supplied to the scan lines GLb1 to GLbk are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

Further, when a selection signal obtained by sequentially shifting pulses is applied to all of the scanning lines GLb1 to GLbk corresponding to the region 101, the sequential shift of pulses is also applied to the scanning lines GLbk + 1 to scanning line GLb2k corresponding to the region 102. Selected signal is provided. In addition, the pulses of the selection signals given to the scanning lines GLbjk + 1 to the scanning lines GLb2k are shifted so that the phase is delayed for a period corresponding to the pulse width. Note that the pulse widths of the selection signals supplied to the scanning lines GLbk + 1 to GLb2k are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

Further, when a selection signal obtained by sequentially shifting the pulses is applied to all of the scanning lines GLbk + 1 to GLb2k corresponding to the region 102, then the sequential shifting of the pulses is also performed to the scanning lines GL2bk + 1 to the scanning lines GLb3k corresponding to the region 103. Selected signal is provided. In addition, the pulses of the selection signals supplied to the scanning lines GLb2k + 1 to the scanning lines GLb3k are shifted so that the phase is delayed for a period corresponding to the pulse width. Note that the pulse widths of the selection signals supplied to the scanning lines GLb2k + 1 to GLb3k are approximately the same as the pulse widths of the first pulse width control signal (PWC1) to the sixth pulse width control signal (PWC6).

Next, in the holding period, the supply of the drive signal or the power supply potential to the second scan line driver circuit 11b is stopped. Specifically, first, the supply of the scan line drive circuit start pulse signal (GSP) is stopped to stop the output of the selection signal from the pulse output circuit in the second scan line drive circuit 11b, and the second The selection by the pulse in all the scanning lines connected to the scanning line driving circuit 11b is terminated. Thereafter, the supply of the power supply potential Vdd to the second scan line driver circuit 11b is stopped. Note that the stop of input or supply means, for example, that a wiring to which a signal or a potential is input is in a floating state or a low-level potential is applied to a wiring to which a signal or a potential is input. . By the above method, it is possible to prevent the second scanning line driving circuit 11b from malfunctioning when the operation is stopped. In addition to the above structure, the second scan line driver circuit first clock signal (GCK1) to the second scan line driver circuit fourth clock signal (GCK4) and the first pulse width control signal (PWC1) are provided. Alternatively, the supply of the sixth pulse width control signal (PWC6) to the second scan line driver circuit 11b may be stopped.

By stopping the supply of the drive signal or power supply potential to the second scan line driver circuit 11b, the scan lines GLb1 to GLbk, the scan lines GLbk + 1 to the scan lines GLb2k, and the scan lines GLb2k + 1 to the scan lines GLb3k Is supplied with a low-level potential.

Note that in the monochrome moving image display period 302, the operation of the second scanning line driving circuit 11 b in the writing period is the same as that in the monochrome still image display period 303.

<First Signal Line Driver Circuit 12a>
FIG. 11A illustrates a structural example of the first signal line driver circuit 12a included in the liquid crystal display device illustrated in FIG. The first signal line driver circuit 12a includes a shift register 120a having first to n-th output terminals and a switching element group that controls supply of image signals (DATA) to the signal lines SLa1 to SLan. 123a.

Specifically, the switching element group 123a includes transistors 121_1 to 121_n. The transistors 121_1 to 121_n each have a first terminal connected to a wiring for supplying an image signal (DATA), and a second terminal connected to each of the signal lines SLa1 to SLan. Gate electrodes of the transistors 121_1 to 121_n are connected to first to nth output terminals, respectively.

Note that the shift register 120a operates in accordance with drive signals such as a signal line driver circuit start pulse signal (SSP1) and a signal line driver circuit clock signal (SCK1), and outputs a signal in which pulses are sequentially shifted to a first output. Output from the terminal to the nth output terminal. When the above signal is input to the gate electrode, the transistors 121_1 to 121_n are sequentially turned on.

FIG. 12A is a diagram illustrating an example of the timing of the image signal (DATA) supplied to the signal line in the full-color image display period 301. In the first signal line driver circuit 12a illustrated in FIG. 11A, as illustrated in FIG. 12A, in the period in which the pulses of the selection signals input to the two scanning lines overlap, An image signal (DATA) corresponding to the appearing scanning line is sampled and input to each signal line. Specifically, the pulse of the selection signal input to the scanning line GLa1 and the pulse of the selection signal input to the scanning line GLak + 1 overlap in a period t4 corresponding to ½ of the pulse width. In the scanning line GLa1 and the scanning line GLak + 1, the pulse appears first in the scanning line GLa1. In the period in which the pulses overlap, the image signal (data1) corresponding to the scanning line GLa1 is sampled among the image signals (DATA) and input to the signal lines SLa1 to SLan.

Similarly, in a period t5, an image signal (datak + 1) corresponding to the scanning line GLak + 1 is sampled and input to the signal lines SLa1 to SLan. In a period t6, the image signal (data2k + 1) corresponding to the scanning line GLa2k + 1 is sampled and input to the signal lines SLa1 to SLan. In a period t7, an image signal (data2) corresponding to the scanning line GLa2 is sampled and input to the signal lines SLa1 to SLan. In addition, the image signal (DATA) is written in the pixel portion by repeating the same operation after the period t8.

That is, the input of the image signal to the signal lines SLa1 to SLa is performed by inputting pixels connected to the scanning line GLas (s is a natural number less than k), then pixels connected to the scanning line GLak + s, and then scanning lines. This is done in the order of pixels connected to GLa2k + s, then pixels connected to scan line GLas + 1.

FIG. 12B is a diagram illustrating an example of the timing of the image signal (DATA) supplied to the signal line in the writing period included in the monochrome moving image display period 302 and the monochrome still image display period 303.

<Second Signal Line Driver Circuit 12b>
FIG. 11B is a diagram illustrating a configuration example of the second signal line driver circuit 12b included in the liquid crystal display device illustrated in FIG. The second signal line driver circuit 12b includes a shift register 120b having first to nth output terminals and a switching element group that controls supply of an image signal (DATA) to the signal lines SLb1 to SLbn. 123b.

Specifically, the switching element group 123b has n transistors. Each transistor has a first terminal connected to a wiring for supplying an image signal (DATA), and a second terminal connected to each of the signal lines SLb1 to SLbn. The gate electrode of the transistor is connected to each of the first output terminal to the nth output terminal.

Note that the shift register 120b operates in accordance with drive signals such as the signal line driver circuit start pulse signal (SSP2) and the signal line driver circuit clock signal (SCK2), and outputs a signal in which the pulses are sequentially shifted to the first output. Output from the terminal to the nth output terminal. When the signal is input to the gate electrode, the n transistors are sequentially turned on.

In the second signal line driver circuit 12b shown in FIG. 11B, as shown in FIG. 12B, in the period in which the pulse of the selection signal input to each scanning line appears, The corresponding image signal (DATA) is sampled and input to each signal line. Specifically, during the period in which the pulse of the selection signal input to the scanning line GLb1 appears, the image signal (data1) corresponding to the scanning line GLb1 is sampled among the image signals (DATA), and the signal line SLb1 is sampled. To the signal line SLbn.

Similarly, an image signal (DATA) is written in the pixel portion by repeating the same operation in each scanning line after the scanning line GLb1.

Note that in the holding period of the monochrome still image display period 303, the signal line driver circuit start pulse signal (SSP2) is supplied to the shift register 120b and the image signal (DATA) is supplied to the second signal line driver circuit 12b. Stop supplying. Specifically, first, sampling of the image signal in the second signal line driving circuit 12b is stopped by stopping the supply of the signal line driving circuit start pulse signal (SSP2). Thereafter, the supply of the image signal to the second signal line driver circuit 12b and the supply of the power supply potential are stopped. By the above method, it is possible to prevent the second signal line driver circuit 12b from malfunctioning when the operation is stopped. Further, in addition to the above structure, the supply of the signal line driver circuit clock signal (SCK2) to the second signal line driver circuit 12b may be stopped.

<Operation example of liquid crystal display device>
FIG. 13 is a diagram illustrating the scanning timing of the selection signal and the lighting timing of the backlight in the above-described liquid crystal display device in the full-color image display period 301. In FIG. 13, the vertical axis represents rows in the pixel portion, and the horizontal axis represents time.

As shown in FIG. 13, in the liquid crystal display device described in this embodiment, after a selection signal is supplied to the scanning line GLa1 in the full-color image display period 301, the selection is performed for the scanning line GLak + 1 of k rows ahead. A driving method for supplying a signal can be used. Therefore, in the same subframe period SF, n pixels connected to the scanning line GLak are sequentially selected from n pixels connected to the scanning line GLa1, and n pixels connected to the scanning line GLak + 1 are selected. By sequentially selecting n pixels connected to the scanning line GLa2k from the pixels, and sequentially selecting n pixels connected to the scanning line GLa3k from the n pixels connected to the scanning line GLa2k + 1, An image signal can be input to each pixel.

Specifically, in FIG. 13, in the first subframe period SF1, an image signal corresponding to red (R) is written to the pixels connected from the scanning line GLa1 to the scanning line GLak, and then connected to the scanning line. Red (R) light is supplied to the pixels. With the above structure, an image corresponding to red (R) can be displayed in the region 101 of the pixel portion corresponding to the scanning line GLa1 to the scanning line GLak.

In addition, in the first subframe period SF1, after an image signal corresponding to green (G) is written to the pixels connected to the scanning line GLa2k from the scanning line GLak + 1, green (G) is added to the pixels connected to the scanning line. G) is supplied. With the above structure, an image corresponding to green (G) can be displayed in the region 102 of the pixel portion corresponding to the scanning line GLak + 1 to the scanning line GLa2k.

In addition, in the first subframe period SF1, after writing an image signal corresponding to blue (B) to the pixels connected to the scan line GLa3k from the scan lines GLa2k + 1, blue (B) is written to the pixels connected to the scan line. B) light is supplied. With the above structure, an image corresponding to blue (B) can be displayed in the region 103 of the pixel portion corresponding to the scanning lines GLa2k + 1 to GLa3k.

Next, in the second subframe period SF2 and the third subframe period SF3, the same operation as in the first subframe period SF1 is repeated. However, in the second subframe period SF2, an image corresponding to blue (B) is displayed in the region 101 of the pixel portion corresponding to the scanning line GLa1 to the scanning line GLak, and corresponding to the scanning line GLa2k from the scanning line GLak + 1. An image corresponding to red (R) is displayed in the pixel area 102, and an image corresponding to green (G) is displayed in the pixel area 103 corresponding to the scanning lines GLa2k + 1 to GLa3k. In the third subframe period SF3, an image corresponding to green (G) is displayed in the region 101 of the pixel portion corresponding to the scanning line GLa1 to the scanning line GLak, and corresponding to the scanning line GLa2k from the scanning line GLak + 1. An image corresponding to blue (B) is displayed in the pixel region 102, and an image corresponding to red (R) is displayed in the pixel region 103 corresponding to the scanning lines GLa2k + 1 to GLa3k.

Then, the first subframe period SF1 to the third subframe period SF3 end in all the scanning lines GLa, that is, one frame period ends, so that a full-color image can be displayed on the pixel portion.

Note that in one embodiment of the present invention, each region may be further divided, and lighting of the backlight may be sequentially started when writing of an image signal is finished in the divided region. For example, after writing an image signal corresponding to red (R) to pixels connected to the scanning line GLa1 from the scanning line GLa1 (h is a natural number equal to or less than k / 4) in the region 101, the scanning line GLah + 1 In parallel with writing the image signal corresponding to red (R) to the pixels connected to the scanning line GLa2h, red (R) light is supplied from the scanning line GLa1 to the pixels connected to the scanning line GLah. May be.

FIG. 14 is a diagram showing the scanning timing of the selection signal and the timing of turning off the backlight in the liquid crystal display device described above in the monochrome still image display period 303. In FIG. 14, the vertical axis represents rows in the pixel portion, and the horizontal axis represents time.

As shown in FIG. 14, in the liquid crystal display device described in this embodiment, a selection signal is sequentially supplied to the scanning lines GLb1 to GLb3k in the monochrome still image display period 303.

Specifically, in FIG. 14, for example, after writing an image signal to the pixels connected to the scanning line GLbh from the scanning line GLb1 in the region 101, the image signal is applied to the pixels connected to the scanning line GLb2h from the scanning line GLbh + 1. In parallel with writing, the supply of light from the light source to the pixels connected to the scanning line GLbh from the scanning line GLb1 is stopped. As a result, a monochrome image can be displayed on the pixel portion using outside light.

Note that in the monochrome moving image display period 302, after the above operation is performed on the pixels connected to the scanning lines GLb1 to GLb3k, the same operation is repeated again so that monochrome images are continuously displayed on the pixel portion. It ’s fine.

<Configuration example 2 of pulse output circuit>
FIG. 19A illustrates another configuration example of the pulse output circuit. The pulse output circuit illustrated in FIG. 19A has a structure in which a transistor 50 is added to the pulse output circuit illustrated in FIG. The transistor 50 has a first terminal connected to a node to which a high power supply potential is applied, and a second terminal connected to the gate electrode of the transistor 32, the gate electrode of the transistor 34, and the gate electrode of the transistor 39. . The gate electrode of the transistor 50 is connected to a reset terminal (Reset).

Note that a high-level potential is input to the reset terminal in a period after the switching of the hue of the backlight in the pixel portion is completed, and a low-level potential is input in other periods. Note that the transistor 50 is a transistor that is turned on when a high-level potential is input thereto. Accordingly, the potential of each node can be initialized in a period after the backlight is turned on, and thus malfunction can be prevented.

Note that in the case of performing the initialization, it is necessary to provide an initialization period between periods in which one image is formed in the pixel portion. In addition, when the backlight is turned off after one image is formed in the pixel portion, the initialization can be performed in a period during which the backlight is turned off.

FIG. 19B illustrates another configuration example of the pulse output circuit. The pulse output circuit illustrated in FIG. 19B has a structure in which a transistor 51 is added to the pulse output circuit illustrated in FIG. The transistor 51 has a first terminal connected to the second terminal of the transistor 31 and the second terminal of the transistor 32, and a second terminal connected to the gate electrode of the transistor 33 and the gate electrode of the transistor 38. The gate electrode of the transistor 51 is connected to a node to which a high power supply potential is applied.

Note that the transistor 51 is off in the periods t1 to t6 illustrated in FIGS. 8B and 8C. Therefore, by adding the transistor 51, the gate electrode of the transistor 33 and the gate electrode of the transistor 38 are connected to the second terminal of the transistor 31 and the second terminal of the transistor 32 in the period t1 to the period t6. It becomes possible to block. Accordingly, in the period included in the period t1 to the period t6, it is possible to reduce the load during the bootstrap operation performed in the pulse output circuit.

FIG. 20A illustrates another configuration example of the pulse output circuit. The pulse output circuit illustrated in FIG. 20A has a structure in which a transistor 52 is added to the pulse output circuit illustrated in FIG. The transistor 52 has a first terminal connected to the gate electrode of the transistor 33 and the second terminal of the transistor 51, and a second terminal connected to the gate electrode of the transistor 38. The gate electrode of the transistor 52 is connected to a node to which a high power supply potential is applied.

By providing the transistor 52, it is possible to reduce the load during the bootstrap operation performed in the pulse output circuit. In particular, when the pulse output circuit raises the potential of the node connected to the gate electrode of the transistor 33 only by capacitive coupling between the source electrode and the gate electrode of the transistor 33, the effect of reducing the load is great.

FIG. 20B illustrates another configuration example of the pulse output circuit. The pulse output circuit illustrated in FIG. 20B has a structure in which the transistor 51 is deleted from the pulse output circuit illustrated in FIG. The transistor 53 has a first terminal connected to the second terminal of the transistor 31, a second terminal of the transistor 32, and a first terminal of the transistor 52, and a second terminal connected to the gate electrode of the transistor 33. The transistor 53 has a gate electrode connected to a node to which a high power supply potential is applied.

By providing the transistor 53, it is possible to reduce the load during the bootstrap operation performed in the pulse output circuit. In addition, it is possible to reduce the influence of the irregular pulse generated in the pulse output circuit on the switching of the transistor 33 and the transistor 38.

As described in this embodiment, a liquid crystal display device according to one embodiment of the present invention can display a color image by dividing a pixel portion into a plurality of regions and sequentially supplying light of different hues in each region. I do. Therefore, when paying attention to a specific time, the hue of light supplied to adjacent regions can be made different from each other. Therefore, it is possible to prevent the images of the respective colors from being individually viewed without being combined, and it is possible to prevent the occurrence of a color break that easily occurs when displaying a moving image.

Note that when a color image is displayed using a plurality of light sources having different hues, it is necessary to sequentially switch the plurality of light sources to emit light, unlike when combining a single color light source and a color filter. The frequency at which the light source is switched needs to be set to a value higher than the frame frequency when a monochromatic light source is used. For example, if the frame frequency when a monochromatic light source is used is 60 Hz, when the field sequential driving is performed using the light sources corresponding to the colors red, green, and blue, the frequency for switching the light source is about 3 Doubled to 180 Hz. Therefore, since the drive circuit is also operated in accordance with the frequency of the light source, the operation is performed at a very high frequency. Therefore, the power consumption in the drive circuit tends to be higher than when a monochromatic light source and a color filter are combined.

However, in one embodiment of the present invention, the period in which the voltage applied to the liquid crystal element is held can be extended by using a transistor with extremely low off-state current. Therefore, the driving frequency when displaying a still image can be made lower than the driving frequency when displaying a moving image. Therefore, a liquid crystal display device that can reduce power consumption can be realized.

(Embodiment 2)
In this embodiment, an example of a liquid crystal display device according to one embodiment of the present invention, in which the panel structure is different from that in Embodiment 1 will be described.

FIG. 15 is a diagram illustrating a configuration example of a liquid crystal display device. The liquid crystal display device illustrated in FIG. 15 includes a pixel portion 60, scanning line driving circuits 61a and 61b, and signal line driving circuits 62a and 62b. In one embodiment of the present invention, the pixel portion 60 is divided into a plurality of regions. Specifically, FIG. 15 illustrates a case where the pixel unit 60 is divided into three regions (regions 601 to 603). Each region has a plurality of pixels 615 arranged in a matrix.

The pixel portion 60 is provided with m scanning lines GLa whose potential is controlled by the scanning line driving circuit 61a and 3 × n signal lines SL whose potential is controlled by the signal line driving circuit 62a. ing. The m scanning lines GLa are divided into a plurality of groups according to the number of regions of the pixel unit 60. For example, in the case of FIG. 15, since the pixel unit 60 is divided into three regions, the m scanning lines GLa are also divided into three groups. The scanning lines GLa belonging to each group are connected to a plurality of pixels 615 included in a region corresponding to the group. Specifically, each scanning line GLa is connected to n pixels 615 arranged in any row among a plurality of pixels 615 arranged in a matrix in each region.

The signal lines SL are also divided into a plurality of groups in accordance with the number of regions included in the pixel portion 60. For example, in the case of FIG. 15, since the pixel unit 60 is divided into three regions, 3 × n signal lines SL are also divided into three groups. The signal lines SL belonging to each group are connected to a plurality of pixels 615 included in a region corresponding to the group.

Specifically, FIG. 15 illustrates a case where 3 × n signal lines SL include n signal lines SLa, n signal lines SLc, and n signal lines SLd. ing. 15 illustrates a case where n signal lines SLa are connected to the pixels 615 arranged in any column among the plurality of pixels 615 arranged in a matrix in the region 601. doing. FIG. 15 illustrates an example in which n signal lines SLc are connected to the pixels 615 arranged in any column among the plurality of pixels 615 arranged in a matrix in the region 602. doing. FIG. 15 illustrates an example in which n signal lines SLd are connected to the pixels 615 arranged in any column among the plurality of pixels 615 arranged in a matrix in the region 603. doing.

<Configuration Example of Scanning Line Driving Circuit 61a and Scanning Line Driving Circuit 61b>
FIG. 16A is a diagram illustrating a configuration example of the scan line driver circuit 61a included in the liquid crystal display device illustrated in FIG. A scan line driver circuit 61a illustrated in FIG. 16A includes shift registers 611 to 613 each including k output terminals. Note that each of the output terminals of the shift register 611 is connected to one of the k scanning lines GLa provided in the region 601, and each of the output terminals of the shift register 612 is provided in the region 602. Each of the output terminals of the shift register 613 is connected to one of the k scanning lines GLa provided in the region 603. That is, the shift register 611 is a shift register that scans the selection signal in the region 601, the shift register 612 is a shift register that scans the selection signal in the region 602, and the shift register 613 scans the selection signal in the region 603. Shift register.

Specifically, when a pulse of a scan line driver circuit start pulse signal (GSP) is input to the shift register 611, the pulses are sequentially supplied to the scan lines GLa1 to GLak every 1/2 cycle in accordance with the pulse. Supply a selection signal to shift. When a pulse of the scan line driver circuit start pulse signal (GSP) is input to the shift register 612, a selection signal that sequentially shifts the pulses to the scan lines GLak + 1 to GLa2k every 1/2 cycle in accordance with the pulses. Supply. When a pulse of the scan line driver circuit start pulse signal (GSP) is input to the shift register 613, a selection signal that sequentially shifts the pulses to the scan lines GLa2k + 1 to GLa3k every 1/2 cycle according to the pulse. Supply.

An operation example of the above-described scanning line driving circuit 61a in the full color image display period 301 will be described with reference to FIG.

Note that in FIG. 17A, a scanning line driver circuit clock signal (GCK), a selection signal input to the scanning lines GLa1 to GLak, a selection signal input to the scanning lines GLak + 1 to GLa2k, and a scanning line The timing chart of the selection signal input into GLa2k + 1 thru | or scanning line GLa3k is shown.

First, the operation of the scanning line driving circuit 61a in the full color image display period 301 will be described. In the full-color image display period 301, the first subframe period SF1 starts in accordance with the pulse of the scan line driver circuit start pulse signal (GSP). In the first subframe period SF1, a selection signal for sequentially shifting the pulse every ½ cycle is supplied to the scanning lines GLa1 to GLak. A selection signal for sequentially shifting the pulses every 1/2 cycle is also supplied to the scanning lines GLak + 1 to GLa2k. In addition, a selection signal for sequentially shifting the pulse every 1/2 cycle is also supplied to the scanning lines GLa2k + 1 to GLa3k.

Then, when a pulse of the scan line driver circuit start pulse signal (GSP) is input again to the scan line driver circuit 61a, the second subframe period SF2 starts in accordance with the pulse. In the second subframe period SF2, similarly to the first subframe period SF1, the pulses are sequentially shifted to the scanning lines GLa1 to GLak, the scanning lines GLak + 1 to GLa2k, and the scanning lines GLa2k + 1 to GLa3k. A selection signal is input.

Then, when the pulse of the scan line driver circuit start pulse signal (GSP) is input again to the scan line driver circuit 61a, the third subframe period SF3 starts in accordance with the pulse. In the third subframe period SF3, similarly to the first subframe period SF1, the pulses are sequentially shifted to the scanning lines GLa1 to GLak, the scanning lines GLak + 1 to GLa2k, and the scanning lines GLa2k + 1 to GLa3k. A selection signal is input.

When the first subframe period SF1 to the third subframe period SF3 end, one frame period ends, and an image is displayed on the pixel portion.

Next, the operation of the scanning line driving circuit 61b in the monochrome still image display period 303 will be described. In the monochrome still image display period 303, the scanning line driving circuit 61b performs the same operation as each subframe period in the full-color image display period 301 in the image signal writing period.

A scan line driver circuit 61b illustrated in FIG. 16B includes a shift register 614 having 3k output terminals. Note that each of the output terminals of the shift register 614 is provided in the k scanning lines GLb provided in the region 601, the k scanning lines GLb provided in the region 602, and the region 603. Connected to any one of the k scanning lines GLb.

Specifically, when the pulse of the scan line driver circuit start pulse signal (GSP) is input, the shift register 614 starts operation according to the pulse and outputs a selection signal in which the pulses are sequentially shifted.

Next, in the holding period, the supply of the drive signal and the power supply potential to the scan line driver circuit 61b is stopped. Specifically, first, by stopping the supply of the scan line drive circuit start pulse signal (GSP), the output of the selection signal from the scan line drive circuit 61b is stopped, and the selection by the pulse in all of the scan lines GLb is performed. End. Thereafter, the supply of the power supply potential to the scanning line driving circuit 61b is stopped. By the above method, it is possible to prevent the scanning line driving circuit 61b from malfunctioning when the operation of the scanning line driving circuit 61b is stopped. Further, in addition to the above structure, the supply of the second scan line driver circuit first clock signal (GCK1) to the second scan line driver circuit fourth clock signal (GCK4) to the scan line driver circuit 61b is stopped. You may do it.

By stopping the supply of the drive signal or power supply potential to the scan line driver circuit 61b, the scan lines GLb1 to GLbk, the scan lines GLbk + 1 to the scan lines GLb2k, and the scan lines GLb2k + 1 to the scan lines GLb3k are low. A level potential is applied.

Note that in the monochrome moving image display period 302, the operation of the scanning line driving circuit 61 b in the writing period is the same as that in the monochrome still image display period 303.

In one embodiment of the present invention, a transistor in which an off-state current is extremely small is used for a pixel, so that a period during which a voltage applied to the liquid crystal element is held can be extended. Therefore, in the monochrome still image display period 303, the holding period shown in FIG. 17B can be secured longer, and the driving frequency of the scanning line driver circuit 61b can be lower than that in the full-color image display period 301. Therefore, a liquid crystal display device that can reduce power consumption can be realized.

<Configuration Example of Signal Line Driver Circuit 62a>
FIG. 18A is a diagram illustrating a configuration example of the signal line driver circuit 62a illustrated in FIG. A signal line driver circuit 62a illustrated in FIG. 18A includes a shift register 620a including first to nth output terminals, an image signal (DATA1) corresponding to a region 601 and an image signal corresponding to a region 602. (DATA2) and a switching element group 623 that controls supply of the image signal (DATA3) corresponding to the region 603 to the signal line SLa, the signal line SLc, and the signal line SLd.

Specifically, the switching element group 623 includes transistors 65a1 to 65an, transistors 65c1 to 65cn, and transistors 65d1 to 65dn.

The first terminals of the transistors 65a1 to 65an are connected to a wiring for supplying an image signal (DATA1), and the second terminals are connected to the signal lines SLa1 to SLan. Gate electrodes of the transistors 65a1 to 65an are connected to a first output terminal to an nth output terminal of the shift register 620a, respectively.

The first terminals of the transistors 65c1 to 65cn are connected to a wiring for supplying an image signal (DATA2), and the second terminals are connected to the signal lines SLc1 to SLcn, respectively. Gate electrodes of the transistors 65c1 to 65cn are connected to a first output terminal to an nth output terminal of the shift register 620a, respectively.

The first terminals of the transistors 65d1 to 65dn are connected to a wiring for supplying an image signal (DATA3), and the second terminals are connected to the signal lines SLd1 to SLdn. Gate electrodes of the transistors 65d1 to 65dn are connected to a first output terminal to an nth output terminal of the shift register 620a, respectively.

Note that the shift register 620a operates according to drive signals such as a signal line driver circuit start pulse signal (SSP1) and a signal line driver circuit clock signal (SCK1), and outputs a signal obtained by sequentially shifting the pulses to the first output. Output from the terminal to the nth output terminal. When the signal is input to the gate electrode, the transistors 65a1 to 65an, the transistors 65c1 to 65cn, and the transistors 65d1 to 65dn are sequentially turned on. Then, an image signal (DATA1) is input to the signal lines SLa1 to SLan, an image signal (DATA2) is input to the signal lines SLc1 to SLcn, and an image signal (DATA3) is input to the signal lines SLd1 to SLdn. The image is input and displayed.

<Configuration Example of Signal Line Driver Circuit 62b>
18B is a diagram illustrating a configuration example of the signal line driver circuit 62b included in the liquid crystal display device illustrated in FIG. The signal line driver circuit 62b includes a shift register 620b having first to nth output terminals and a switching element group 624 that controls supply of an image signal (DATA) to the signal lines SLb1 to SLbn. Have.

The switching element group 624 includes transistors 65b1 to 65bn. The first terminals of the transistors 65b1 to 65bn are connected to a wiring for supplying an image signal (DATA4), and the second terminals are connected to the signal lines SLb1 to SLbn, respectively. Gate electrodes of the transistors 65b1 to 65bn are connected to the first output terminal to the nth output terminal, respectively.

Note that the shift register 620b operates in accordance with drive signals such as a signal line driver circuit start pulse signal (SSP2) and a signal line driver circuit clock signal (SCK2), and outputs a signal in which pulses are sequentially shifted to a first output. Output from the terminal to the nth output terminal. When the signal is input to the gate electrode, the transistors 65b1 to 65bn are sequentially turned on.

Note that in the holding period of the monochrome still image display period 303, the signal line driver circuit start pulse signal (SSP2) is supplied to the shift register 620b and the image signal (DATA4) is supplied to the signal line driver circuit 62b. Stop. Specifically, first, the sampling of the image signal in the signal line driving circuit 62b is stopped by stopping the supply of the signal line driving circuit start pulse signal (SSP2). Thereafter, the supply of the image signal to the signal line driver circuit 62b and the supply of the power supply potential are stopped. By the above method, it is possible to prevent the signal line driver circuit 62b from malfunctioning when the operation is stopped. Further, in addition to the above configuration, the supply of the signal line driver circuit clock signal (SCK2) to the signal line driver circuit 62b may be stopped.

This embodiment can be implemented in combination with any of the above embodiments as appropriate.

(Embodiment 3)
In this embodiment, a method for manufacturing a transistor including an oxide semiconductor will be described.

First, as illustrated in FIG. 21A, an insulating film 701 is formed over an insulating surface of a substrate 700, and a gate electrode 702 is formed over the insulating film 701.

A substrate that can be used as the substrate 700 only needs to have a light-transmitting property, and there is no particular limitation on the substrate, but it should have at least heat resistance enough to withstand heat treatment performed later. Is required. For example, as the substrate 700, a glass substrate, a quartz substrate, a ceramic substrate, or the like manufactured by a fusion method or a float method can be used. As the glass substrate, a glass substrate having a strain point of 730 ° C. or higher is preferably used when the temperature of the subsequent heat treatment is high. A substrate made of a synthetic resin having flexibility such as plastic generally tends to have a lower heat resistant temperature than the above substrate, but can be used as long as it can withstand the processing temperature in the manufacturing process. .

The insulating film 701 is formed using a material that can withstand the temperature of heat treatment in a later manufacturing process. Specifically, silicon oxide, silicon nitride, silicon nitride oxide, silicon oxynitride, aluminum nitride, aluminum oxide, gallium oxide, or the like is preferably used for the insulating film 701.

Note that in this specification, oxynitride is a substance having a higher oxygen content than nitrogen in the composition, and nitride oxide has a nitrogen content higher than oxygen in the composition. Means a substance.

As a material of the gate electrode 702, a metal material such as molybdenum, titanium, chromium, tantalum, tungsten, neodymium, or scandium, a conductive film using an alloy material mainly containing these metal materials, or a nitride of these metals is used. It can be used in layers or in layers. Note that aluminum or copper can also be used as the metal material as long as it can withstand the temperature of heat treatment performed in a later step. Aluminum or copper is preferably used in combination with a refractory metal material in order to avoid heat resistance and corrosive problems. As the refractory metal material, molybdenum, titanium, chromium, tantalum, tungsten, neodymium, scandium, or the like can be used.

The thickness of the gate electrode 702 is 10 nm to 400 nm, preferably 100 nm to 200 nm. In this embodiment, a gate electrode 702 is formed by forming a conductive film for a gate electrode with a thickness of 150 nm by a sputtering method using a tungsten target and then processing (patterning) the conductive film into a desired shape by etching. To do. Note that it is preferable that the end portion of the formed gate electrode has a tapered shape because coverage with a gate insulating film stacked thereover is improved. Note that the resist mask may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Next, as illustrated in FIG. 21B, a gate insulating film 703 is formed over the gate electrode 702, and then an island-shaped oxide semiconductor film 704 is formed over the gate insulating film 703 so as to overlap with the gate electrode 702. To do.

The gate insulating film 703 is formed using a silicon oxide film, a silicon nitride film, a silicon oxynitride film, a silicon nitride oxide film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, a oxynitride oxide, using a plasma CVD method, a sputtering method, or the like. An aluminum film, a hafnium oxide film, a tantalum oxide film, or a gallium oxide film can be formed as a single layer or stacked layers. The gate insulating film 703 preferably contains as little moisture, impurities as hydrogen and oxygen as possible. In the case of forming a silicon oxide film by a sputtering method, a silicon target or a quartz target is used as a target, and oxygen or a mixed gas of oxygen and argon is used as a sputtering gas.

Since an oxide semiconductor purified by removing impurities is extremely sensitive to interface states and interface charges, the interface between the purified oxide semiconductor and the gate insulating film 703 is important. . Therefore, the gate insulating film (GI) in contact with the highly purified oxide semiconductor is required to have high quality.

For example, high-density plasma CVD using μ-wave (frequency: 2.45 GHz) is preferable because a high-quality insulating film with high density and high withstand voltage can be formed. This is because when the highly purified oxide semiconductor and the high-quality gate insulating film are in close contact with each other, the interface state can be reduced and interface characteristics can be improved.

Needless to say, another film formation method such as a sputtering method or a plasma CVD method can be used as long as a high-quality insulating film can be formed as the gate insulating film 703. In any case, any film can be used as long as it can reduce the interface state between the gate insulating film and the oxide semiconductor and form a favorable interface, as well as good film quality as the gate insulating film.

In this embodiment, the gate insulating film 703 having a structure in which an aluminum oxide film with a thickness of 100 nm formed by a sputtering method is stacked over a silicon nitride film with a thickness of 50 nm formed by a sputtering method is formed. . The thickness of the gate insulating film 703 may be set as appropriate depending on characteristics required for the transistor, and may be approximately 350 nm to 400 nm.

Note that the gate insulating film 703 is in contact with an oxide semiconductor formed later. Since an oxide semiconductor adversely affects characteristics when hydrogen is contained, the gate insulating film 703 preferably contains no hydrogen, a hydroxyl group, or moisture. In order to prevent hydrogen, a hydroxyl group, and moisture from being contained in the gate insulating film 703 as much as possible, as a pretreatment for film formation, the substrate 700 over which the gate electrode 702 is formed is preheated in a preheating chamber of a sputtering apparatus, It is preferable that impurities such as moisture or hydrogen adsorbed on the substrate 700 be desorbed and exhausted. Note that the preheating temperature is 100 ° C. or higher and 400 ° C. or lower, preferably 150 ° C. or higher and 300 ° C. or lower. Note that a cryopump is preferable as an exhaustion unit provided in the preheating chamber. Note that this preheating treatment can be omitted.

The island-shaped oxide semiconductor film can be formed by processing the oxide semiconductor film formed over the gate insulating film 703 into a desired shape. The thickness of the oxide semiconductor film is 2 nm to 200 nm, preferably 3 nm to 50 nm, more preferably 3 nm to 20 nm. The oxide semiconductor film is formed by a sputtering method using an oxide semiconductor as a target. The oxide semiconductor film can be formed by a sputtering method in a rare gas (eg, argon) atmosphere, an oxygen atmosphere, or a rare gas (eg, argon) and oxygen mixed atmosphere.

In this embodiment, a 30-nm-thick In—Ga— film obtained by a sputtering method using an oxide semiconductor target containing In (indium), Ga (gallium), and Zn (zinc) as the oxide semiconductor film. A thin film of a Zn—O-based oxide semiconductor is used as the oxide semiconductor film. Examples of the target include a molar ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 2, In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 1, or In ₂ O. _A target of ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 4 can be used. The filling rate of the target containing In, Ga, and Zn is 90% to 100%, preferably 95% to less than 100%.

In this embodiment mode, the substrate is held in a processing chamber kept under reduced pressure, a sputtering gas from which hydrogen and moisture have been removed while introducing residual moisture in the processing chamber is introduced, and the substrate 700 is formed using the above target. An oxide semiconductor film is formed. At the time of film formation, the substrate temperature may be 100 ° C. or higher and 600 ° C. or lower, preferably 200 ° C. or higher and 400 ° C. or lower. By forming the film while heating the substrate, the concentration of impurities contained in the formed oxide semiconductor film can be reduced. Further, damage due to sputtering is reduced. In order to remove moisture remaining in the treatment chamber, an adsorption-type vacuum pump is preferably used. For example, it is preferable to use a cryopump, an ion pump, or a titanium sublimation pump. The exhaust means may be a turbo pump provided with a cold trap. When a processing chamber is exhausted using a cryopump, for example, a compound containing a hydrogen atom (more preferably a compound containing a carbon atom) such as a hydrogen atom or water (H ₂ O) is exhausted. The concentration of impurities contained in the formed oxide semiconductor film can be reduced.

As an example of the film forming conditions, the distance between the substrate and the target is 100 mm, the pressure is 0.6 Pa, the direct current (DC) power source is 0.5 kW, and the oxygen (oxygen flow rate is 100%) atmosphere is applied. Note that a pulse direct current (DC) power source is preferable because dust generated in film formation can be reduced and the film thickness can be made uniform.

Note that in order to prevent the oxide semiconductor film from containing hydrogen, a hydroxyl group, and moisture as much as possible, as a pretreatment for film formation, the substrate 700 over which the gate insulating film 703 is formed in the preheating chamber of the sputtering apparatus is preliminarily used. It is preferable that impurities such as water or hydrogen adsorbed on the substrate 700 be heated and desorbed and exhausted. Note that the preheating temperature is 100 ° C. or higher and 400 ° C. or lower, preferably 150 ° C. or higher and 300 ° C. or lower. In addition, a cryopump is preferable as the exhaust means provided in the preheating chamber. Note that this preheating treatment can be omitted. Further, this preheating may be similarly performed on the substrate 700 over which the conductive films 705 and 706 are formed before the insulating film 707 to be formed later.

Note that the etching for forming the island-shaped oxide semiconductor film 704 may be dry etching or wet etching, or both may be used. As an etching gas used for dry etching, a gas containing chlorine (chlorine-based gas such as chlorine (Cl ₂ ), boron trichloride (BCl ₃ ), silicon tetrachloride (SiCl ₄ ), carbon tetrachloride (CCl ₄ ), or the like) Is preferred. Gas containing fluorine (fluorine-based gas such as carbon tetrafluoride (CF ₄ ), sulfur hexafluoride (SF ₆ ), nitrogen trifluoride (NF ₃ ), trifluoromethane (CHF ₃ ), etc.), bromide Hydrogen (HBr), oxygen (O ₂ ), a gas obtained by adding a rare gas such as helium (He) or argon (Ar) to these gases, or the like can be used.

As the dry etching method, a parallel plate RIE (Reactive Ion Etching) method or an ICP (Inductively Coupled Plasma) etching method can be used. Etching conditions (such as the amount of power applied to the coil-type electrode, the amount of power applied to the substrate-side electrode, the substrate-side electrode temperature, etc.) are adjusted as appropriate so that the desired processed shape can be etched.

As an etchant used for wet etching, ITO-07N (manufactured by Kanto Chemical Co., Inc.) may be used.

A resist mask for forming the island-shaped oxide semiconductor film 704 may be formed by an inkjet method. When the resist mask is formed by an ink-jet method, a manufacturing cost can be reduced because a photomask is not used.

Note that an oxide semiconductor film formed by sputtering or the like may contain a large amount of moisture or hydrogen (including a hydroxyl group) as an impurity. Since moisture or hydrogen easily forms a donor level, it is an impurity for an oxide semiconductor. Therefore, in one embodiment of the present invention, the island-shaped oxide semiconductor film 704 is subjected to a reduced pressure atmosphere in order to reduce (dehydrate or dehydrogenate) impurities such as moisture or hydrogen in the oxide semiconductor film. 20 ppm (dew point conversion) when measured with an inert gas atmosphere such as nitrogen or rare gas, oxygen gas atmosphere, or ultra-dry air (CRDS (cavity ring down laser spectroscopy) type dew point meter) The island-shaped oxide semiconductor film 704 is subjected to heat treatment under an atmosphere of −55 ° C. or less, preferably 1 ppm or less, preferably 10 ppb or less.

By performing heat treatment on the island-shaped oxide semiconductor film 704, moisture or hydrogen in the island-shaped oxide semiconductor film 704 can be eliminated. Specifically, heat treatment may be performed at a temperature of 250 ° C. to 750 ° C., preferably 400 ° C. to less than the strain point of the substrate. For example, it may be performed at 500 ° C. for about 3 minutes to 6 minutes. When the RTA method is used for the heat treatment, dehydration or dehydrogenation can be performed in a short time, and thus the treatment can be performed even at a temperature exceeding the strain point of the glass substrate.

In this embodiment, an electric furnace which is one of heat treatment apparatuses is used.

Note that the heat treatment apparatus is not limited to an electric furnace, and may include a device for heating an object to be processed by heat conduction or heat radiation from a heating element such as a resistance heating element. For example, a rapid thermal annealing (RTA) device such as a GRTA (Gas Rapid Thermal Anneal) device or an LRTA (Lamp Rapid Thermal Anneal) device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp. The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

Note that in the heat treatment, moisture, hydrogen, or the like is preferably not contained in nitrogen or a rare gas such as helium, neon, or argon. Alternatively, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration is 1 ppm). Or less, preferably 0.1 ppm or less).

Through the above steps, the concentration of hydrogen in the island-shaped oxide semiconductor film 704 can be reduced and highly purified. Accordingly, stabilization of the oxide semiconductor film can be achieved. In addition, an oxide semiconductor film with a low band density due to hydrogen and a wide band gap can be formed by heat treatment at a glass transition temperature or lower. Therefore, a transistor can be manufactured using a large-area substrate, and mass productivity can be improved. The heat treatment can be performed at any time after the oxide semiconductor film is formed.

Note that in the case of heating an oxide semiconductor film, a plate-like crystal may be formed on the surface of the oxide semiconductor film, depending on a material of the oxide semiconductor film and heating conditions. The plate-like crystal is preferably a single crystal having a c-axis orientation substantially perpendicular to the surface of the oxide semiconductor film. Note that in the case where the surface of the gate insulating film 703 in contact with the oxide semiconductor film is uneven, the plate-like crystal is a polycrystalline body. Therefore, it is desirable that the surface of the gate insulating film 703 be as flat as possible.

Next, as illustrated in FIG. 21C, the conductive film 705 and the conductive film 706 functioning as a source electrode and a drain electrode, and the conductive film 705, the conductive film 706, and the island-shaped oxide semiconductor film 704 are formed. An insulating film 707 is formed.

The conductive films 705 and 706 are formed by forming a conductive film by a sputtering method or a vacuum evaporation method so as to cover the island-shaped oxide semiconductor film 704 and then patterning the conductive film by etching or the like. be able to.

The conductive films 705 and 706 are in contact with the island-shaped oxide semiconductor film 704. As a material of the conductive film to be the conductive films 705 and 706, an element selected from aluminum, chromium, copper, tantalum, titanium, molybdenum, and tungsten, an alloy including the above-described elements as components, or the above-described elements are used. An alloy film or the like in combination. Alternatively, a high melting point metal film such as chromium, tantalum, titanium, molybdenum, or tungsten may be stacked below or above the metal film such as aluminum or copper. Aluminum or copper is preferably used in combination with a refractory metal material in order to avoid problems of heat resistance and corrosion. As the refractory metal material, molybdenum, titanium, chromium, tantalum, tungsten, neodymium, scandium, yttrium, or the like can be used.

The conductive film may have a single-layer structure or a stacked structure including two or more layers. For example, a single layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, a titanium film, an aluminum film laminated on the titanium film, and a titanium film formed on the titanium film. Examples include a three-layer structure.

Alternatively, the conductive film to be the conductive films 705 and 706 may be formed using a conductive metal oxide. As the conductive metal oxide, indium oxide, tin oxide, zinc oxide, indium tin oxide alloy, indium zinc oxide alloy, or a material in which silicon or silicon oxide is included in the metal oxide material can be used.

In the case where heat treatment is performed after formation of the conductive film, the conductive film preferably has heat resistance enough to withstand the heat treatment.

Note that each material and etching conditions are adjusted as appropriate so that the island-shaped oxide semiconductor film 704 is not removed as much as possible when the conductive film is etched. Depending on the etching conditions, a part of the exposed portion of the island-shaped oxide semiconductor film 704 may be etched to form a groove (a depressed portion).

In this embodiment, a titanium film is used for the conductive film. Therefore, the conductive film can be selectively wet etched using a solution containing ammonia and aqueous hydrogen peroxide (ammonium hydrogen peroxide), but the island-shaped oxide semiconductor film 704 is also partially etched. Specifically, an aqueous solution in which hydrogen peroxide water, pure water, and ammonium hydroxide are mixed at a volume ratio of 2: 1: 1 is used as the solution containing ammonium perhydrate. Alternatively, the conductive film may be dry-etched using a gas containing chlorine (Cl ₂ ), boron chloride (BCl ₃ ), or the like.

Note that in order to reduce the number of photomasks used in the photolithography process and the number of processes, the etching process may be performed using a resist mask formed by a multi-tone mask that gives multi-level intensity to transmitted light. A resist mask formed using a multi-tone mask has a shape with a plurality of thicknesses, and the shape can be further deformed by etching. Therefore, the resist mask can be used for a plurality of etching processes for processing into different patterns. . Therefore, a resist mask corresponding to at least two kinds of different patterns can be formed by using one multi-tone mask. Therefore, the number of exposure masks can be reduced, and the corresponding photolithography process can be reduced, so that the process can be simplified.

Note that before the insulating film 707 is formed, plasma treatment using a gas such as N ₂ O, N ₂ , or Ar is performed on the island-shaped oxide semiconductor film 704. Adsorbed water or the like attached to the surface of the island-shaped oxide semiconductor film 704 exposed by this plasma treatment is removed. Further, plasma treatment may be performed using a mixed gas of oxygen and argon.

The insulating film 707 preferably contains as little moisture and impurities as hydrogen, and may be a single-layer insulating film or a plurality of stacked insulating films. When hydrogen is contained in the insulating film 707, the hydrogen penetrates into the oxide semiconductor film, or hydrogen extracts oxygen in the oxide semiconductor film, so that the back channel portion of the island-shaped oxide semiconductor film 704 has low resistance. (N-type) may occur, and a parasitic channel may be formed. Therefore, it is important not to use hydrogen in the deposition method so that the insulating film 707 contains as little hydrogen as possible. It is preferable to use a material having a high barrier property for the insulating film 707. For example, as the insulating film having a high barrier property, a silicon nitride film, a silicon nitride oxide film, an aluminum nitride film, an aluminum nitride oxide film, an aluminum oxide film, a gallium oxide film, or the like can be used. By using an insulating film having a high barrier property, moisture can be formed in the island-shaped oxide semiconductor film 704, the gate insulating film 703, or the interface between the island-shaped oxide semiconductor film 704 and another insulating film and the vicinity thereof. Alternatively, impurities such as hydrogen can be prevented from entering.

In this embodiment, the insulating film 707 having a structure in which an aluminum oxide film with a thickness of 100 nm formed by a sputtering method is stacked over a gallium oxide film with a thickness of 200 nm formed by a sputtering method is formed. The substrate temperature at the time of film formation may be from room temperature to 300 ° C., and is 100 ° C. in this embodiment. The insulating film 707 preferably contains a large amount of oxygen, to an extent exceeding the stoichiometric composition ratio, preferably more than 1 to 2 times the stoichiometric composition ratio (greater than 1 and twice as much) Less than) oxygen. In this manner, when the insulating film 707 includes excess oxygen, oxygen can be supplied to the interface of the island-shaped oxide semiconductor film 704 so that oxygen vacancies can be reduced.

Note that heat treatment may be performed after the insulating film 707 is formed. The heat treatment is preferably performed at 200 ° C. to 400 ° C., for example, 250 ° C. to 350 ° C. in an atmosphere of nitrogen, ultra-dry air, or a rare gas (such as argon or helium). The gas should have a water content of 20 ppm or less, preferably 1 ppm or less, preferably 10 ppb or less. In this embodiment, for example, heat treatment is performed at 250 ° C. for one hour in a nitrogen atmosphere. Alternatively, before the conductive films 705 and 706 are formed, high-temperature and short-time RTA treatment may be performed as in the previous heat treatment performed on the oxide semiconductor film for reducing moisture or hydrogen. good. By performing heat treatment after the insulating film 707 containing oxygen is provided, even if oxygen vacancies are generated in the island-shaped oxide semiconductor film 704 due to the previous heat treatment, Oxygen is supplied to the oxide semiconductor film 704 having a shape. By supplying oxygen to the island-shaped oxide semiconductor film 704, oxygen vacancies serving as donors in the island-shaped oxide semiconductor film 704 can be reduced and the stoichiometric composition ratio can be satisfied. is there. The island-shaped oxide semiconductor film 704 preferably contains oxygen in an amount exceeding the stoichiometric composition ratio. As a result, the island-shaped oxide semiconductor film 704 can be made closer to i-type, variation in electric characteristics of the transistor due to oxygen vacancies can be reduced, and electrical characteristics can be improved. The timing for performing this heat treatment is not particularly limited as long as it is after the formation of the insulating film 707. For example, the heat treatment at the time of forming the resin film or the resistance of the light-transmitting conductive film is reduced. By combining with heat treatment, the island-shaped oxide semiconductor film 704 can be made to be i-type without increasing the number of steps.

In addition, by performing heat treatment on the island-shaped oxide semiconductor film 704 in an oxygen atmosphere, oxygen is added to the oxide semiconductor so that oxygen vacancies serving as donors in the island-shaped oxide semiconductor film 704 are reduced. Also good. The temperature of the heat treatment is, for example, 100 ° C. or higher and lower than 350 ° C., preferably 150 ° C. or higher and lower than 250 ° C. The oxygen gas used for the heat treatment under the oxygen atmosphere preferably does not contain water, hydrogen, or the like. Alternatively, the purity of the oxygen gas introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (that is, the impurity concentration in oxygen is 1 ppm or less, preferably 0.1 ppm). Or less).

Alternatively, oxygen vacancies serving as donors may be reduced by adding oxygen to the island-shaped oxide semiconductor film 704 by an ion implantation method, an ion doping method, or the like. For example, oxygen that is plasmatized with a microwave of 2.45 GHz may be added to the island-shaped oxide semiconductor film 704.

Note that after the conductive film is formed over the insulating film 707, the back gate electrode may be formed in a position overlapping with the island-shaped oxide semiconductor film 704 by patterning the conductive film. When the back gate electrode is formed, it is desirable to form an insulating film so as to cover the back gate electrode. The back gate electrode can be formed using a material and a structure similar to those of the gate electrode 702, the conductive films 705, and 706.

The thickness of the back gate electrode is 10 nm to 400 nm, preferably 100 nm to 200 nm. For example, after a conductive film having a structure in which a titanium film, an aluminum film, and a titanium film are stacked is formed, a resist mask is formed by a photolithography method or the like, and unnecessary portions are removed by etching, so that the conductive film is desired. It is preferable to form a back gate electrode by processing (patterning) into the shape. By making the back gate electrode function as a light-shielding film, light deterioration of the transistor, for example, light negative bias deterioration can be reduced, and reliability can be improved.

Through the above process, the transistor 708 is formed.

The transistor 708 includes a gate electrode 702, a gate insulating film 703 over the gate electrode 702, an island-shaped oxide semiconductor film 704 overlapping with the gate electrode 702 over the gate insulating film 703, and an island-shaped oxide semiconductor film. A pair of conductive films 705 or 706 is formed over 704. Further, the transistor 708 may include an insulating film 707 in its constituent elements. A transistor 708 illustrated in FIG. 21C has a channel-etched structure in which part of the island-shaped oxide semiconductor film 704 is etched between the conductive films 705 and 706.

Note that although the transistor 708 is described as a single-gate transistor, a multi-gate transistor having a plurality of channel formation regions by including a plurality of gate electrodes 702 that are electrically connected as necessary. Can also be formed.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 4)
In this embodiment, structural examples of transistors are described. Note that portions and processes having the same or similar functions to those in the above embodiment can be performed in a manner similar to that in the above embodiment, and repetitive description in this embodiment is omitted. Detailed description of the same part is also omitted.

In the transistor 2450 illustrated in FIG. 22A, a gate electrode 2401 is formed over a substrate 2400, a gate insulating film 2402 is formed over the gate electrode 2401, and an oxide semiconductor film 2403 is formed over the gate insulating film 2402. A source electrode 2405a and a drain electrode 2405b are formed over the oxide semiconductor film 2403. An insulating film 2407 is formed over the oxide semiconductor film 2403, the source electrode 2405a, and the drain electrode 2405b. Further, the protective insulating film 2409 may be formed over the insulating film 2407. The transistor 2450 is one of bottom-gate transistors and one of inverted staggered transistors.

In the transistor 2460 illustrated in FIG. 22B, a gate electrode 2401 is formed over a substrate 2400, a gate insulating film 2402 is formed over the gate electrode 2401, and an oxide semiconductor film 2403 is formed over the gate insulating film 2402. A channel protective layer 2406 is formed over the oxide semiconductor film 2403, and a source electrode 2405 a and a drain electrode 2405 b are formed over the channel protective layer 2406 and the oxide semiconductor film 2403. Further, a protective insulating film 2409 may be formed over the source electrode 2405a and the drain electrode 2405b. The transistor 2460 is one of bottom-gate transistors called a channel protection type (also referred to as a channel stop type) and is also an inverted staggered transistor. The channel protective layer 2406 can be formed using a material and a method similar to those of other insulating films.

In the transistor 2470 illustrated in FIG. 22C, a base film 2436 is formed over the substrate 2400, an oxide semiconductor film 2403 is formed over the base film 2436, and a source is formed over the oxide semiconductor film 2403 and the base film 2436. An electrode 2405a and a drain electrode 2405b are formed, a gate insulating film 2402 is formed over the oxide semiconductor film 2403, the source electrode 2405a, and the drain electrode 2405b, and a gate electrode 2401 is formed over the gate insulating film 2402. Further, a protective insulating film 2409 may be formed over the gate electrode 2401. The transistor 2470 is one of top-gate transistors.

In a transistor 2480 illustrated in FIG. 22D, a first gate electrode 2411 is formed over a substrate 2400, a first gate insulating film 2413 is formed over the first gate electrode 2411, and the first gate insulating film is formed. An oxide semiconductor film 2403 is formed over the film 2413, and a source electrode 2405a and a drain electrode 2405b are formed over the oxide semiconductor film 2403 and the first gate insulating film 2413. In addition, a second gate insulating film 2414 is formed over the oxide semiconductor film 2403, the source electrode 2405a, and the drain electrode 2405b, and a second gate electrode 2412 is formed over the second gate insulating film 2414. Further, the protective insulating film 2409 may be formed over the second gate electrode 2412.

The transistor 2480 has a structure in which the transistor 2450 and the transistor 2470 are combined. The first gate electrode 2411 and the second gate electrode 2412 can be electrically connected to function as one gate electrode. One of the first gate electrode 2411 and the second gate electrode 2412 may be simply referred to as a gate electrode, and the other may be referred to as a back gate electrode.

By changing the potential of the back gate electrode, the threshold voltage of the transistor can be changed. The back gate electrode is formed so as to overlap with a channel formation region of the oxide semiconductor film 2403. The back gate electrode may be in a floating state where it is electrically insulated, or in a state where a potential is applied. In the latter case, the back gate electrode may be given the same potential as the gate electrode, or may be given a fixed potential such as ground. By controlling the potential applied to the back gate electrode, the threshold voltage of the transistor 2480 can be controlled.

In addition, when the oxide semiconductor film 2403 is covered with the back gate electrode, light can be prevented from entering the oxide semiconductor film 2403 from the back gate electrode side. Therefore, light degradation of the oxide semiconductor film 2403 can be prevented, and degradation of characteristics such as shift of the threshold voltage of the transistor can be prevented.

An insulating film in contact with the oxide semiconductor film 2403 (in this embodiment, the gate insulating film 2402, the insulating film 2407, the channel protective layer 2406, the base film 2436, the first gate insulating film 2413, and the second gate insulating film 2414 Is preferably an insulating material containing a Group 13 element and oxygen. Many oxide semiconductor materials contain a Group 13 element, and an insulating material containing a Group 13 element has good compatibility with an oxide semiconductor. By using this for an insulating film in contact with the oxide semiconductor film, oxidation can be performed. The state of the interface with the physical semiconductor film can be kept good.

An insulating material containing a Group 13 element means that the insulating material contains one or more Group 13 elements. Examples of the insulating material containing a Group 13 element include gallium oxide, aluminum oxide, aluminum gallium oxide, and gallium aluminum oxide. Here, aluminum gallium oxide indicates that the aluminum content (atomic%) is higher than gallium content (atomic%), and gallium aluminum oxide means that the gallium aluminum content (atomic%) contains aluminum. Indicates more than the amount (atomic%).

For example, when an insulating film is formed in contact with an oxide semiconductor film containing gallium, the interface characteristics between the oxide semiconductor film and the insulating film can be kept favorable by using a material containing gallium oxide for the insulating film. . For example, when the oxide semiconductor film and the insulating film containing gallium oxide are provided in contact with each other, hydrogen pileup at the interface between the oxide semiconductor film and the insulating film can be reduced. Note that in the case where an element in the same group as the constituent elements of the oxide semiconductor film is used for the insulating film, a similar effect can be obtained. For example, it is also effective to form an insulating film using a material containing aluminum oxide. Note that aluminum oxide has a characteristic that water does not easily permeate, and thus the use of the material is preferable in terms of preventing water from entering the oxide semiconductor film.

The insulating film in contact with the oxide semiconductor film 2403 is preferably made to have a higher oxygen content than the stoichiometric composition ratio by heat treatment in an oxygen atmosphere, oxygen doping, or the like. Oxygen doping means adding oxygen to the bulk. The term “bulk” is used for the purpose of clarifying that oxygen is added not only to the surface of the thin film but also to the inside of the thin film. The oxygen dope includes oxygen plasma dope in which plasma oxygen is added to the bulk. Further, oxygen doping may be performed using an ion implantation method or an ion doping method.

For example, in the case where gallium oxide is used as the insulating film in contact with the oxide semiconductor film 2403, the composition of gallium oxide is changed to Ga ₂ O _X (X = 3 + α, 0 <α by performing heat treatment in an oxygen atmosphere or oxygen doping. <1).

In the case where aluminum oxide is used as the insulating film in contact with the oxide semiconductor film 2403, the composition of the aluminum oxide is changed to Al ₂ O _X (X = 3 + α, 0 <α by performing heat treatment in an oxygen atmosphere or oxygen doping. <1).

In the case where gallium aluminum oxide (aluminum gallium oxide) is used as the insulating film in contact with the oxide semiconductor film 2403, the composition of gallium aluminum oxide (aluminum gallium oxide) is changed by performing heat treatment in an oxygen atmosphere or oxygen doping. _{Ga X Al 2-X O 3} + α (0 <X <2,0 <α <1) can be.

By performing the oxygen doping treatment, an insulating film having a region where oxygen is higher than the stoichiometric composition ratio can be formed. When the insulating film including such a region is in contact with the oxide semiconductor film, excess oxygen in the insulating film is supplied to the oxide semiconductor film, and the oxide semiconductor film or the interface between the oxide semiconductor film and the insulating film is supplied. Oxygen deficiency can be reduced, and the oxide semiconductor film can be made to be an I-type oxide semiconductor or an oxide semiconductor close to I-type.

Note that the insulating film having a region where oxygen is higher than the stoichiometric composition ratio is one of the insulating film in contact with the oxide semiconductor film 2403 and the insulating film in the upper layer or the insulating film in the lower layer. However, it is preferable to use it for both insulating films. An insulating film having a region where oxygen is higher than that in the stoichiometric composition ratio is used as an insulating film located above and below the insulating film in contact with the oxide semiconductor film 2403 so that the oxide semiconductor film 2403 is interposed therebetween. Thus, the above effect can be further enhanced.

The insulating film used for the upper layer or the lower layer of the oxide semiconductor film 2403 may be an insulating film having the same constituent element in the upper layer and the lower layer, or may be an insulating film having different constituent elements. For example, the upper layer and the lower layer may be gallium oxide having a composition of Ga ₂ O _X (X = 3 + α, 0 <α <1), and one of the upper layer and the lower layer may have a composition of Ga ₂ O _X (X = 3 + α, 0 <Α <1) may be gallium oxide, and the other may be aluminum oxide having a composition of Al ₂ O _X (X = 3 + α, 0 <α <1).

The insulating film in contact with the oxide semiconductor film 2403 may be a stack of insulating films having a region where oxygen is higher than the stoichiometric composition ratio. For example, gallium oxide having a composition of Ga ₂ O _X (X = 3 + α, 0 <α <1) is formed over the oxide semiconductor film 2403, and the composition of the film is Ga _X Al _{2 -X} O _{3 + α} (0 < You may form the gallium aluminum oxide (aluminum gallium oxide) of X <2, 0 <α <1). Note that the lower layer of the oxide semiconductor film 2403 may be a stack of insulating films having a region where oxygen is higher than the stoichiometric composition ratio, and both the upper layer and the lower layer of the oxide semiconductor film 2403 may be stoichiometric. An insulating film having a region where oxygen is higher than the composition ratio may be stacked.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 5)
In this embodiment, one embodiment of a substrate used in a liquid crystal display device according to one embodiment of the present invention will be described with reference to FIGS.

First, the layer to be peeled 6116 is formed over the substrate 6200 with the peeling layer 6201 interposed therebetween (see FIG. 23A).

As the substrate 6200, a quartz substrate, a sapphire substrate, a ceramic substrate, a glass substrate, a metal substrate, or the like can be used. Note that these substrates can be used to form an element such as a transistor with high accuracy by using a substrate having a thickness that does not clearly indicate flexibility. The level that does not clearly indicate flexibility means that the glass substrate is usually used at the time of manufacturing a liquid crystal display, or has a higher elastic modulus.

The separation layer 6201 is formed by tungsten (W), molybdenum (Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), sputtering, plasma CVD, coating, printing, or the like. An element selected from cobalt (Co), zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), silicon (Si), Alternatively, a layer formed of an alloy material containing an element as a main component or a compound material containing an element as a main component is formed as a single layer or a stacked layer.

In the case where the separation layer 6201 has a single-layer structure, a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum is preferably formed. Alternatively, a layer containing tungsten oxide or oxynitride, a layer containing molybdenum oxide or oxynitride, or a layer containing an oxide or oxynitride of a mixture of tungsten and molybdenum is formed. Note that the mixture of tungsten and molybdenum corresponds to, for example, an alloy of tungsten and molybdenum.

In the case where the separation layer 6201 has a stacked structure, preferably, a metal layer is formed as a first layer and a metal oxide layer is formed as a second layer. Typically, a tungsten layer, a molybdenum layer, or a layer containing a mixture of tungsten and molybdenum is formed as a first layer, and an oxide, nitride, or oxynitride of tungsten, molybdenum, or a mixture of tungsten and molybdenum is formed as a second layer. An oxide or a nitrided oxide is preferably formed. The second metal oxide layer is formed by forming an oxide layer (for example, one that can be used as an insulating layer such as silicon oxide) on the first metal layer to oxidize the metal on the surface of the metal layer. You may apply that a thing is formed.

The layer to be peeled 6116 includes elements necessary as an element substrate, such as a transistor, an interlayer insulating film, a wiring, a pixel electrode, and a counter electrode, a light-shielding film, and an alignment film depending on circumstances. These can be formed on the release layer 6201 as usual. Since these materials, manufacturing methods, structures, and the like are the same as those described in the above embodiments, description thereof is omitted. As described above, the transistor and the electrode can be accurately manufactured using a known material and method.

Next, after the layer 6116 to be peeled is bonded to the temporary support substrate 6202 using the peeling adhesive 6203, the layer 6116 to be peeled is peeled off from the peeling layer 6201 of the substrate 6200 and transferred (see FIG. 23B). Thus, the layer to be peeled 6116 is provided on the temporary support substrate side. Note that in this specification, the step of transferring the release layer from the substrate to the temporary support substrate is referred to as a transfer step.

As the temporary support substrate 6202, a glass substrate, a quartz substrate, a sapphire substrate, a ceramic substrate, a metal substrate, or the like can be used. Further, a plastic substrate having heat resistance that can withstand subsequent processing temperatures may be used.

In addition, the peeling adhesive 6203 used here is soluble in water or a solvent, or can be plasticized by irradiation with ultraviolet rays or the like. Adhesive that can be separated is used.

Note that various methods can be appropriately used for the transfer step to the temporary support substrate 6202. For example, in the case where a film including a metal oxide film is formed on the side in contact with the layer to be peeled 6116 as the peeling layer 6201, the metal oxide film is weakened by crystallization, and the layer to be peeled 6116 is peeled from the substrate 6200. can do. In the case where an amorphous silicon film containing hydrogen is formed as the peeling layer 6201 between the substrate 6200 and the layer to be peeled 6116, the amorphous silicon film containing hydrogen is removed by laser light irradiation or etching. Thus, the layer to be peeled 6116 can be peeled from the substrate 6200. In the case where a film containing nitrogen, oxygen, hydrogen, or the like (eg, an amorphous silicon film containing hydrogen, a hydrogen-containing alloy film, an oxygen-containing alloy film, or the like) is used as the separation layer 6201, a laser is used for the separation layer 6201. By irradiation with light, nitrogen, oxygen, or hydrogen contained in the separation layer 6201 is released as a gas, so that separation of the separation layer 6116 and the substrate 6200 can be promoted. As another method, the layer to be peeled 6116 may be peeled from the substrate 6200 by infiltrating a liquid into the interface between the peeling layer 6201 and the layer to be peeled 6116. There is also a method in which the peeling layer 6201 is formed of tungsten and peeling is performed while etching the peeling layer 6201 with a mixed solution of ammonia water and hydrogen peroxide water.

Moreover, the transposition process can be performed more easily by combining a plurality of the above peeling methods. Laser irradiation, etching of the release layer with gas or solution, mechanical removal with a sharp knife or scalpel, etc. are partially performed to make the release layer and the peelable layer easy to peel off, and then physically This is the process of peeling with a strong force (by machine etc.). In the case where the peeling layer 6201 is formed using a stacked structure of a metal and a metal oxide, the peeling layer 6201 may be physically peeled off from the peeling layer due to a groove formed by laser light irradiation, a scratch by a sharp knife, a knife, or the like. It becomes easy.

Moreover, when performing these peeling, you may carry out, applying liquids, such as water.

Other methods for separating the layer to be peeled 6116 from the substrate 6200 include a method of removing the substrate 6200 on which the layer to be peeled 6116 is formed by mechanical polishing, a solution, NF ₃ , BrF ₃ , A method of removing by etching with a halogen fluoride gas such as ClF ₃ can also be used. In this case, the separation layer 6201 is not necessarily provided.

Subsequently, the transfer substrate 6110 is bonded to the surface of the peeled layer 6201 that is peeled off from the substrate 6200 or the exposed layer 6116 using the first adhesive layer 6111 using an adhesive different from the peeling adhesive 6203 ( (See FIG. 23C).

As a material for the first adhesive layer 6111, various curable adhesives such as a photocurable adhesive such as an ultraviolet curable adhesive, a reactive curable adhesive, a thermosetting adhesive, or an anaerobic adhesive are used. be able to.

As the transfer substrate 6110, various substrates having high toughness are used, and for example, an organic resin film or a metal substrate can be preferably used. A substrate having high toughness is a substrate that has excellent impact resistance and is not easily damaged. Since an organic resin film is lightweight and a thin metal substrate is lightweight, the weight can be significantly reduced as compared with the case of using a normal glass substrate. By using such a substrate, a liquid crystal display device that is light and hardly damaged can be manufactured.

In the case of a transmissive or transflective liquid crystal display device, a substrate having high toughness and a property of transmitting visible light may be used as the transfer substrate 6110. Examples of the material constituting such a substrate include polyester resins such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN), acrylic resins, polyacrylonitrile resins, polyimide resins, polymethyl methacrylate resins, and polycarbonate resins (PCs). ), Polyether sulfone resin (PES), polyamide resin, cycloolefin resin, polystyrene resin, polyamideimide resin, polyvinyl chloride resin and the like. Since these organic resin substrates have high toughness, they are excellent in impact resistance and are not easily damaged. In addition, since these organic resin films are lightweight, it is possible to manufacture a liquid crystal display device that is much lighter than an ordinary glass substrate. In this case, it is preferable that the transfer substrate 6110 further includes a metal plate 6206 provided with an opening in a portion overlapping at least a region through which light of each pixel is transmitted. With this configuration, it is possible to configure the transfer substrate 6110 that has high toughness, high impact resistance, and is not easily damaged while suppressing dimensional changes. Further, by reducing the thickness of the metal plate 6206, a transfer substrate 6110 that is lighter than a conventional glass substrate can be formed. By using such a substrate, a liquid crystal display device that is light and hardly damaged can be manufactured. (See FIG. 23D).

After that, the temporary support substrate 6202 is separated from the layer to be peeled 6116. The peeling adhesive 6203 is formed using a material that can separate the temporary support substrate 6202 and the layer to be peeled 6116 when necessary. Therefore, the temporary support substrate 6202 may be separated by a method suitable for the material. Note that the backlight is irradiated as shown by arrows in the drawing (see FIG. 23E).

Through the above steps, the layer to be peeled 6116 from the transistor to the pixel electrode (a counter electrode, a light-shielding film, an alignment film, or the like may be provided as necessary) can be formed over the transfer substrate 6110. An element substrate that is lightweight and has high impact resistance can be manufactured.

<Modification>
The liquid crystal display device having the above-described configuration is one embodiment of the present invention, and the following liquid crystal display device having a configuration different from the liquid crystal display device having the above-described configuration is also included in the present invention. After the transfer step (FIG. 23B), before the transfer substrate 6110 is attached, a metal plate 6206 may be attached to the exposed surface of the release layer 6201 or the peeled layer 6116 (FIG. 23 ( C ′)). In this case, a barrier layer 6207 is preferably provided in between in order to prevent contaminants from the metal plate 6206 from adversely affecting the characteristics of the transistor in the layer to be peeled 6116. In the case of providing the barrier layer 6207, the metal plate 6206 may be attached after the barrier layer 6207 is provided on the surface of the exposed peeling layer 6201 or the peeled layer 6116. The barrier layer 6207 may be formed using an inorganic material, an organic material, or the like, and typically includes silicon nitride. However, the barrier layer 6207 is not limited thereto as long as contamination of the transistor can be prevented. The barrier layer is formed using a light-transmitting material or a film that is at least light-transmitting, such as a thin film that transmits light. Note that the metal plate 6206 may be bonded by forming a second adhesive layer (not shown) using an adhesive different from the peeling adhesive 6203.

After that, a first adhesive layer 6111 is formed on the surface of the metal plate 6206, a transfer substrate 6110 is attached (FIG. 23D ′), and the temporary support substrate 6202 is separated from the layer to be peeled 6116 (FIG. 23 ( E ′)) makes it possible to manufacture a light-weight and high impact-resistant element substrate. The backlight is irradiated as shown by the arrows in the drawing.

A light-weight and high impact-resistant liquid crystal display device is manufactured by sandwiching the light-weight and high-impact-resistant element substrate thus manufactured and a counter substrate with a liquid crystal layer sandwiched between them and a sealing material. Can do. As the counter substrate, a substrate having large toughness and a property of transmitting visible light (similar to a plastic substrate that can be used for the transfer substrate 6110) can be used. If necessary, a polarizing plate, a light shielding film, a counter electrode, and an alignment film may be provided thereon. As a method for forming the liquid crystal layer, a dispenser method, an injection method, or the like can be applied as in the prior art.

The light-weight and high impact-resistant liquid crystal display device manufactured as described above can be used to manufacture fine elements such as transistors on a glass substrate with relatively good dimensional stability. Since the same manufacturing method can be applied, even a fine element can be formed with high accuracy. Therefore, it is possible to provide a light-weight liquid crystal display device that can provide high-definition and high-quality images while having impact resistance.

Furthermore, the liquid crystal display device manufactured as described above can be flexible.

This embodiment can be implemented in combination with any of the above embodiments as appropriate.

(Embodiment 6)
FIG. 24 shows a top view of a pixel as an example. A cross section taken along chain line A1-A2 in FIG. 24 is shown in FIG. A cross section taken along chain line B1-B2 in FIG. 24 is shown in FIG.

24 and 25, the same reference numerals are used for portions common to FIG. 2B. A pixel illustrated in FIG. 25A includes a conductive film 501 functioning as a scanning line GLa, a conductive film 502 functioning as a signal line SLa, a conductive film 503 functioning as a wiring COM, and the first pixel transistor 16a. And a conductive film 504 functioning as two terminals. The conductive film 501 also functions as the gate electrode of the first pixel transistor 16a illustrated in FIG. The conductive film 502 also functions as the first terminal of the first pixel transistor 16a.

The conductive films 501 and 503 can be formed by processing one conductive film formed over the substrate 500 having an insulating surface into a desired shape. A gate insulating film 506 is formed over the conductive films 501 and 503. Further, the conductive films 502 and 504 can be formed by processing one conductive film formed over the gate insulating film 506 into a desired shape.

Further, the active layer 507 of the first pixel transistor 16 a is formed over the gate insulating film 506 at a position overlapping with the conductive film 501. As shown in FIG. 25A, the active layer 507 preferably has a structure overlapping with the conductive film 501 functioning as a gate electrode. By adopting the above structure, it is possible to prevent deterioration of the oxide semiconductor in the active layer 507 due to light incident from the substrate 500 side, and thus deterioration of characteristics such as shift of the threshold voltage of the first pixel transistor 16a. Can be prevented.

Further, in the pixel illustrated in FIG. 25A, an insulating film 512 and an insulating film 513 are sequentially formed so as to cover the active layer 507, the conductive film 502, and the conductive film 504. A pixel electrode 505 located in the transmission region is formed over the insulating film 513, and the conductive film 504 and the pixel electrode 505 are connected to each other through a contact hole formed in the insulating film 512 and the insulating film 513. ing.

Note that a portion where the conductive film 503 functioning as the wiring COM overlaps with the conductive film 504 with the gate insulating film 506 interposed therebetween functions as the first capacitor element 17a.

In this embodiment, the insulating film 508 is formed between the conductive film 501 and the gate insulating film 506. Since the insulating film 508 is provided between the conductive film 501 and the conductive film 502, parasitic capacitance generated between the conductive film 501 and the conductive film 502 can be suppressed by the insulating film 508.

In this embodiment, the insulating film 509 is formed between the conductive film 503 and the gate insulating film 506. A spacer 510 is formed on the pixel electrode 505 at a position overlapping with the insulating film 509.

A counter electrode 515 is formed over the substrate 514, and a liquid crystal layer 516 containing liquid crystal is provided between the pixel electrode 505 and the counter electrode 515. A first liquid crystal element 18 a is formed in a portion where the pixel electrode 505, the counter electrode 515, and the liquid crystal layer 516 overlap.

The pixel electrode 505 and the counter electrode 515 include, for example, indium tin oxide containing silicon oxide (ITSO), indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide to which gallium is added ( A light-transmitting conductive material such as GZO) can be used.

Note that an alignment film may be provided as appropriate between the pixel electrode 505 and the liquid crystal layer 516 or between the counter electrode 515 and the liquid crystal layer 516. The alignment film can be formed using an organic resin such as polyimide or polyvinyl alcohol, and the surface thereof is subjected to an alignment treatment such as rubbing for aligning liquid crystal molecules in a certain direction. The rubbing can be performed by rotating a roller wrapped with a cloth such as nylon so as to contact the alignment film and rubbing the surface of the alignment film in a certain direction. Note that it is also possible to directly form an alignment film having alignment characteristics by an evaporation method using an inorganic material such as silicon oxide without performing an alignment treatment.

In addition, liquid crystal injection performed for forming the liquid crystal layer 516 may use a dispenser type (dropping type) or a dip type (pumping type).

Note that on the substrate 514, in order to prevent the disclination due to the disorder of the alignment of the liquid crystal between the pixels from being visually recognized, or to prevent the diffused light from entering the adjacent pixels, A light-shielding film 517 that can shield light is provided. For the light-shielding film 517, an organic resin containing a black pigment such as carbon black or low-order titanium oxide having an oxidation number smaller than that of titanium dioxide can be used. Alternatively, the light-blocking film 517 can be formed using a film using chromium.

In addition, by providing the light-shielding film 517 so as to overlap with the active layer 507 of the first pixel transistor 16a, the oxide semiconductor in the active layer 507 is prevented from being deteriorated by light incident from the substrate 514 side. It is possible to prevent deterioration of characteristics such as a shift of the threshold voltage of one pixel transistor 16a. Further, light shielding may be performed by disposing a reflective electrode of an adjacent pixel so as to overlap with the active layer 507 of the first pixel transistor 16a. In that case, the positional accuracy of the bonding between the substrate 514 and the substrate 500 is improved. The active layer can be shielded from light without providing a margin and without increasing the number of steps.

The liquid crystal display device having the pixel structure of FIG. 24 has a reflective region where the pixel electrode which is the reflective electrode 525 shown in FIG. 25B is arranged, in addition to the transmissive region shown in FIG.

Alternatively, the surface of the insulating film 513 may be selectively etched so that the surface of the insulating film 513 has an uneven shape, so that the reflective electrode 525 has an uneven shape. When the surface of the reflective electrode 525 has irregularities, incident external light is diffusely reflected, and better display can be performed. Therefore, visibility in display is improved.

The pixel illustrated in FIG. 25B includes a conductive film 521 functioning as the scan line GLb, a conductive film 522 functioning as the signal line SLb, a conductive film 523 functioning as the wiring COM, and the second pixel transistors 16b. And a conductive film 524 functioning as two terminals. The conductive film 521 also functions as the gate electrode of the second pixel transistor 16b illustrated in FIG. The conductive film 522 also functions as the first terminal of the second pixel transistor 16b.

Note that a portion where the conductive film 523 functioning as the wiring COM and the conductive film 524 overlap with the gate insulating film 506 interposed therebetween functions as the second capacitor 17 b.

In addition, by providing the reflective electrode 525 so as to overlap with the active layer 527 of the second pixel transistor 16b, it is possible to prevent the oxide semiconductor in the active layer 527 from deteriorating due to the stray light incident from the substrate 514 side. Thus, it is possible to prevent deterioration of characteristics such as a shift of the threshold voltage of the second pixel transistor 16b.

Note that in the case where the driver circuit is formed on the panel, the transistor used in the driver circuit is also shielded by the gate electrode or the shielding film, thereby preventing deterioration in characteristics such as a shift in the threshold voltage of the transistor. be able to.

25A and 25B, a structure in which the pixel electrode 505 (or the reflective electrode 525) and the counter electrode 515 overlap with each other with the liquid crystal layer 516 interposed therebetween is positioned in the transmission region (reflection region) of the liquid crystal display device. Although the first liquid crystal element 18a or the second liquid crystal element 18b is described as an example, the liquid crystal display device according to one embodiment of the present invention is not limited to this structure. The pixel electrode and the counter electrode may be formed over the same substrate as in an IPS liquid crystal element or a liquid crystal element using a blue phase.

FIG. 27 shows an example in which the pixel configuration is partly different from those in FIGS. FIG. 27B is a cross-sectional view immediately after the pixel electrode 505 is manufactured.

A cross section taken along chain line C1-C2 in FIG. 27A, which is a top view of the pixel, is shown in FIG. Note that in FIGS. 27A and 27B, portions common to FIGS. 24 and 25 are denoted by the same reference numerals.

In the pixel configuration in FIG. 27A, the reflective electrode 526 of the adjacent pixel is disposed so as to overlap with the active layer 507 of the first pixel transistor 16a in order to more reliably prevent light from entering the active layer 507. This is an example of performing light shielding.

By disposing the reflective electrode 526 of the adjacent pixel so as to overlap the active layer 507 of the first pixel transistor 16a, it is possible to prevent the oxide semiconductor in the active layer 507 from deteriorating due to the stray light, and thus the first pixel transistor 16a. It is possible to prevent the deterioration of characteristics such as a shift of the threshold voltage of the pixel transistor 16a. Further, the second pixel transistor 16 b electrically connected to the reflective electrode 525 is shielded from light when the active layer 527 is sandwiched between the reflective electrode 525 and the conductive film 521. With this structure, stray light strikes the active layer 527 of the second pixel transistor 16b, thereby preventing characteristic deterioration due to threshold voltage shift.

As shown in FIG. 27B, the reflective electrode 526 and the reflective electrode 525 are provided over the insulating film 512, and the insulating film 513 is formed using a planarization insulating film so as to cover the reflective electrode 526 and the reflective electrode 525. Is provided. A stacked structure in which the pixel electrode 505 is provided over the insulating film 513 is formed. Accordingly, as shown in FIG. 27A, the pixel electrode 505 and the reflective electrode 525 can be partially overlapped with each other through the insulating film 513, and the area of the transmissive region is enlarged, so that the pixel structure shown in FIG. High aperture ratio.

In addition, as illustrated in FIG. 27B, the reflective electrode 526 is formed over the insulating film 512 with unevenness, and an uneven shape can be formed on the surface of the reflective electrode 526. When the surface of the reflective electrode 526 has unevenness, incident external light is diffusely reflected, and better display can be performed. Therefore, visibility in display is improved.

Next, a liquid crystal display device according to one embodiment of the present invention will be described with reference to FIGS. 26A is a top view of a panel in which a substrate 4001 and a counter substrate 4006 are bonded to each other with a sealant 4005, and FIG. 26B is a cross-sectional view taken along dashed line AA ′ in FIG. It corresponds to.

A sealant 4005 is provided so as to surround the pixel portion 4002 provided over the substrate 4001 and the scan line driver circuit 4004. A counter substrate 4006 is provided over the pixel portion 4002 and the scan line driver circuit 4004. Therefore, the pixel portion 4002 and the scan line driver circuit 4004 are sealed together with the liquid crystal 4007 by the substrate 4001, the sealant 4005, and the counter substrate 4006.

Further, the substrate 4021 over which the signal line driver circuit 4003 is formed is mounted in a region different from the region surrounded by the sealant 4005 over the substrate 4001. FIG. 26B illustrates a transistor 4009 included in the signal line driver circuit 4003.

In addition, the pixel portion 4002 and the scan line driver circuit 4004 provided over the substrate 4001 include a plurality of transistors. FIG. 26B illustrates a transistor 4010a, a transistor 4010b, and a transistor 4022 included in the pixel portion 4002. The transistor 4010a, the transistor 4010b, and the transistor 4022 include an oxide semiconductor in a channel formation region. The light-blocking film 4040 formed over the counter substrate 4006 overlaps with the channel formation region of the transistor 4022. When the transistor 4022 is shielded from light, deterioration of the oxide semiconductor due to light can be prevented, and deterioration of characteristics such as shift of the threshold voltage of the transistor 4022 can be prevented.

Further, the light shielding metal film 4013 overlaps the channel formation region of the transistor 4010a in the same process as the routing wiring 4014 made of a metal material. By shielding the transistor 4010a with the light-shielding metal film 4013, deterioration of the oxide semiconductor due to light can be prevented, and deterioration of characteristics such as shift of the threshold voltage of the transistor 4010a can be prevented. The light-shielding metal film 4013 may be a floating electrode, an electrode electrically connected to the oxide semiconductor of the transistor 4010a, or an electrically connected to the gate electrode of the transistor 4010a. It may be an electrode.

Although the number of steps increases, a light shielding resin film containing a black pigment such as carbon black is formed at a position overlapping with a channel formation region of the transistor 4010a by using an inkjet method or the like instead of the light shielding metal film 4013. It may be shielded from light.

In addition, the pixel electrode 4030a formed of a light-transmitting conductive film is electrically connected to the transistor 4010a. The counter electrode 4031 is formed on the counter substrate 4006. A portion where the pixel electrode 4030a, the counter electrode 4031, and the liquid crystal 4007 overlap corresponds to the liquid crystal element 4011a in the transmissive region.

In addition, the pixel electrode 4030b which is a reflective electrode is electrically connected to the transistor 4010b. A portion where the pixel electrode 4030b, the counter electrode 4031, and the liquid crystal 4007 overlap corresponds to the liquid crystal element 4011b in the reflective region. A pixel electrode 4030b which is a reflective electrode overlaps with a channel formation region of the transistor 4010b. By shielding the transistor 4010b from light, deterioration of the oxide semiconductor due to light can be prevented, and deterioration of characteristics such as shift of the threshold voltage of the transistor 4010b can be prevented.

A spacer 4035 is provided to control the distance (cell gap) between the pixel electrodes 4030a and 4030b and the counter electrode 4031. Note that FIG. 26B illustrates the case where the spacer 4035 is formed by patterning an insulating film; however, a spherical spacer may be used.

In addition, a variety of signals and potentials are supplied to the signal line driver circuit 4003, the scan line driver circuit 4004, and the pixel portion 4002 from a connection terminal 4016 through lead wirings 4014 and 4015. The connection terminal 4016 is electrically connected to a terminal included in the FPC 4018 through an anisotropic conductive film 4019.

Note that glass, ceramics, or plastics can be used for the substrate 4001, the counter substrate 4006, and the substrate 4021. Examples of the plastic include an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a polyester film, an acrylic resin film, and the like. A sheet having a structure in which an aluminum foil is sandwiched between PVF films can also be used.

Note that a light-transmitting material such as a glass plate, a plastic, a polyester film, or an acrylic film is used for the substrate positioned in the light extraction direction from the liquid crystal element 4011.

This embodiment can be implemented in appropriate combination with any of the other embodiments.

(Embodiment 7)
In this embodiment, two kinds of transistors, a transistor 951 and a transistor 952 having a back gate electrode, are manufactured using the manufacturing method described in the other embodiments, and threshold voltages before and after the optical negative bias test are manufactured. (Vth) The result of evaluating the amount of change is shown.

First, a stack structure and a manufacturing method of the transistor 951 are described with reference to FIG. A stacked film of a silicon nitride film (thickness: 200 nm) and a silicon oxynitride film (thickness: 400 nm) was formed as a base film 936 over the substrate 900 by a CVD method. Next, a stacked film of a tantalum nitride film (thickness 30 nm) and a tungsten film (thickness 100 nm) was formed over the base film 936 by sputtering, and the gate electrode 901 was formed by selective etching.

Next, a silicon oxynitride film (thickness: 30 nm) was formed as the gate insulating film 902 over the gate electrode 901 by a high-density plasma CVD method.

Next, an oxide semiconductor film (thickness: 30 nm) was formed over the gate insulating film 902 by an sputtering method using an In—Ga—Zn—O-based oxide semiconductor target. Subsequently, the oxide semiconductor film was selectively etched, so that an island-shaped oxide semiconductor film 903 was formed.

Next, first heat treatment was performed at 450 ° C. for 60 minutes in a nitrogen atmosphere.

Next, a stacked film of a titanium film (thickness 100 nm), an aluminum film (thickness 200 nm), and a titanium film (thickness 100 nm) is formed over the oxide semiconductor film 903 by a sputtering method and selectively etched. Thus, a source electrode 905a and a drain electrode 905b were formed.

Next, a silicon oxide film was formed as the insulating film 907 by a sputtering method in contact with part of the oxide semiconductor film 903 over the source electrode 905a and the drain electrode 905b.

Next, a second heat treatment was performed at 250 ° C. for 60 minutes in a nitrogen atmosphere.

Next, a polyimide resin layer (thickness: 2.0 μm) was formed as the insulating film 908 over the insulating film 907.

Next, a third heat treatment was performed at 250 ° C. for 60 minutes in a nitrogen atmosphere.

A transistor 952 illustrated in FIG. 29B can be manufactured similarly to the transistor 951. Note that the transistor 951 is different in that a back gate electrode 912 is formed between the insulating film 907 and the insulating film 908. The back gate electrode 912 is formed by selectively forming a stacked film of a titanium film (thickness: 100 nm), an aluminum film (thickness: 200 nm), and a titanium film (thickness: 100 nm) on the insulating film 907 by sputtering. It was formed by etching. The back gate electrode 912 was electrically connected to the source electrode 905a.

In both the transistors 951 and 952, the channel length was 3 μm and the channel width was 20 μm.

Next, an optical negative bias test performed on the transistors 951 and 952 manufactured in this embodiment will be described.

The light negative bias test is a kind of acceleration test, and the change in characteristics of a transistor under an environment where light is irradiated can be evaluated in a short time. In particular, the amount of change in Vth of the transistor in the optical negative bias test is an important index for examining the reliability. In the optical negative bias test, it can be said that the smaller the amount of change in Vth, the higher the reliability of the transistor. The amount of change in Vth before and after the optical negative bias test is preferably 1 V or less, and more preferably 0.5 V or less.

Specifically, in the negative optical bias test, the temperature of the substrate on which the transistor is formed (substrate temperature) is maintained constant, the source electrode and the drain electrode of the transistor are set to the same potential, and the gate electrode is irradiated with light. Is applied by applying a potential lower than that of the source electrode and the drain electrode for a predetermined time.

The stress intensity of the light negative bias test can be determined by the light irradiation conditions, the substrate temperature, the electric field strength applied to the gate insulating film, and the electric field application time. The electric field strength applied to the gate insulating film is determined by dividing the potential difference between the gate electrode, the source electrode, and the drain electrode by the thickness of the gate insulating film. For example, if the electric field strength applied to the gate insulating film having a thickness of 100 nm is to be 2 MV / cm, the potential difference may be 20V.

Note that a test in which a potential higher than the potential of the source electrode and the drain electrode is applied to the gate electrode in an environment where light is irradiated is referred to as an optical positive bias test. However, since transistor characteristic fluctuations are more likely to occur, this embodiment evaluates with an optical negative bias test.

In the negative optical bias test in this embodiment, the substrate temperature was room temperature (25 ° C.), the electric field strength applied to the gate insulating film 902 was 2 MV / cm, and the light irradiation and electric field application time were 1 hour. The light irradiation conditions were as follows: Asahi Spectroscopic Xenon light source “MAX-302” was used, with a peak wavelength of 400 nm (half width 10 nm) and an irradiance of 326 μW / cm ² .

Prior to the negative light bias test, first, initial characteristics of the transistor to be tested were measured. In this embodiment mode, the substrate temperature is set to room temperature (25 ° C.), the voltage between the source electrode and the drain electrode (hereinafter referred to as drain voltage or Vd) is set to 3 V, and the voltage between the source electrode and the gate electrode (hereinafter referred to as gate voltage). Or Vg) was changed from −5 V to +5 V, and a change characteristic of a current flowing between the source electrode and the drain electrode (hereinafter referred to as a drain current or Id), that is, a Vg-Id characteristic was measured.

Next, light irradiation is started from the insulating film 908 side, the potential of the source electrode and the drain electrode of the transistor is set to 0 V, and the strength of the electric field applied to the gate insulating film 902 of the transistor is 2 MV / cm. A negative voltage was applied to. Here, since the thickness of the gate insulating film 902 of the transistor is 30 nm, −6 V is applied to the gate electrode 901 and the state is maintained for one hour. Here, the application time is 1 hour, but the time may be appropriately changed according to the purpose.

Next, the application of voltage was terminated, and the Vg-Id characteristics were measured under the same conditions as the measurement of the initial characteristics while irradiating light, and the Vg-Id characteristics after the optical negative bias test were obtained.

Here, the definition of Vth in the present embodiment will be described with reference to FIG. The horizontal axis in FIG. 30 shows the gate voltage on a linear scale, and the vertical axis shows the square root of the drain current (hereinafter also referred to as √Id) on the linear scale. A curve 921 is a curve (hereinafter also referred to as a √Id curve) in which the value of Id in the Vg-Id characteristic is expressed by a square root.

First, a √Id curve (curve 921) is obtained from the measured Vg-Id curve. Next, a tangent 924 of the point on the √Id curve where the differential value of the √Id curve is maximized is obtained. Next, the tangent 924 is stretched, and Vg when Id is 0 A on the tangent 924, that is, the value of the gate voltage axis intercept 925 of the tangent 924 is defined as Vth.

FIG. 31 shows Vg-Id characteristics of the transistor 951 and the transistor 952 before and after the optical negative bias test. 31A and 31B, the horizontal axis represents the gate voltage (Vg), and the vertical axis represents the drain current (Id) with respect to the gate voltage on a logarithmic scale.

FIG. 31A shows Vg-Id characteristics of the transistor 951 before and after the optical negative bias test. The initial characteristic 931 is the Vg-Id characteristic of the transistor 951 before the optical negative bias test, and the post-test characteristic 932 is the Vg-Id characteristic of the transistor 951 after the optical negative bias test. The Vth of the initial characteristic 931 was 1.01V, and the Vth of the post-test characteristic 932 was 0.44V.

FIG. 31B illustrates Vg-Id characteristics of the transistor 952 before and after the optical negative bias test. FIG. 31C is an enlarged view of the portion 945 in FIG. The initial characteristic 941 is the Vg-Id characteristic of the transistor 952 before the optical negative bias test, and the post-test characteristic 942 is the Vg-Id characteristic of the transistor 952 after the optical negative bias test. The Vth of the initial characteristic 941 was 1.16V, and the Vth of the post-test characteristic 942 was 1.10V. Note that since the back gate electrode 912 of the transistor 952 is electrically connected to the source electrode 905a, the potentials of the back gate electrode 912 and the source electrode 905a are the same.

In FIG. 31A, in the post-test characteristic 932, Vth is changed by 0.57 V in the negative direction as compared with the initial characteristic 931. In FIG. 31B, the post-test characteristic 942 is different from the initial characteristic 941. Thus, Vth changes by 0.06 V in the negative direction. Both the transistor 951 and the transistor 952 have a change amount of Vth of 1 V or less, and it can be confirmed that the transistors are highly reliable. In addition, it can be confirmed that the transistor 952 provided with the back gate electrode 912 has a change amount of Vth of 0.1 V or less and is more reliable than the transistor 951.

By using the liquid crystal display device according to one embodiment of the present invention, an electronic device that can display an image with high image quality can be provided. Alternatively, by using the liquid crystal display device according to one embodiment of the present invention, an electronic device with low power consumption can be provided. In particular, in the case of a portable electronic device in which it is difficult to constantly receive power supply, the addition of the liquid crystal display device according to one embodiment of the present invention to its components can also provide an advantage that the continuous use time is increased. .

A liquid crystal display device according to one embodiment of the present invention includes a display device, a notebook personal computer, and an image reproduction device including a recording medium (typically, a recording medium such as a DVD: Digital Versatile Disc) is reproduced and the image is displayed. A device having a display capable of being used). In addition, as an electronic device in which the liquid crystal display device according to one embodiment of the present invention can be used, a mobile phone, a portable game machine, a portable information terminal, an electronic book, a video camera, a digital still camera, a goggle display (head mount) Display), navigation system, sound reproduction device (car audio, digital audio player, etc.), copier, facsimile, printer, printer multifunction device, automatic teller machine (ATM), vending machine, and the like. Specific examples of these electronic devices are shown in FIGS.

FIG. 28A illustrates an electronic book, which includes a housing 7001, a display portion 7002, and the like. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7002. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7002, an electronic book capable of displaying an image with high image quality or an electronic book with low power consumption can be provided. In addition, since a liquid crystal display device can be made flexible by manufacturing a panel using a flexible substrate and also making the touch panel flexible, it is flexible, light and easy to use. Books can be provided.

FIG. 28B illustrates a display device, which includes a housing 7011, a display portion 7012, a support base 7013, and the like. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7012. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7012, a display device capable of displaying an image with high image quality or a display device with low power consumption can be provided. The display device includes all information display devices for personal computers, TV broadcast reception, advertisement display, and the like.

FIG. 28C illustrates an automatic teller machine that includes a housing 7021, a display portion 7022, a coin slot 7023, a bill slot 7024, a card slot 7025, a passbook slot 7026, and the like. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7022. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7022, an automatic teller machine that can display an image with high image quality or an automatic teller machine with low power consumption is provided. Can do.

FIG. 28D illustrates a portable game machine including a housing 7031, a housing 7032, a display portion 7033, a display portion 7034, a microphone 7035, speakers 7036, operation keys 7037, a stylus 7038, and the like. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7033 and the display portion 7034. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7033 and the display portion 7034, a portable game machine capable of displaying an image with high image quality or a portable game machine with low power consumption is provided. can do. Note that although the portable game machine illustrated in FIG. 28D includes two display portions 7033 and 7034, the number of display portions included in the portable game device is not limited thereto.

FIG. 28E illustrates a mobile phone, which includes a housing 7041, a display portion 7042, an audio input portion 7043, an audio output portion 7044, operation keys 7045, a light receiving portion 7046, and the like. An external image can be captured by converting the light received by the light receiving unit 7046 into an electrical signal. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7042. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7042, a mobile phone capable of displaying an image with high image quality or a mobile phone with low power consumption can be provided.

FIG. 28F illustrates a portable information terminal including a housing 7051, a display portion 7052, operation keys 7053, and the like. In the portable information terminal illustrated in FIG. 28F, a modem may be incorporated in the housing 7051. The liquid crystal display device according to one embodiment of the present invention can be used for the display portion 7052. By using the liquid crystal display device according to one embodiment of the present invention for the display portion 7052, a portable information terminal capable of displaying an image with high image quality or a portable information terminal with low power consumption can be provided.

This example can be implemented in combination with any of the above embodiments as appropriate.

DESCRIPTION OF SYMBOLS 10 Pixel part 11a, 11b Scan line drive circuit 12a, 12b Signal line drive circuit 15 Pixel 16a, 16b Transistor 17a, 17b Capacitance element 18a, 18b Liquid crystal element 20 Pulse output circuit 100 Liquid crystal display device 101 Area 102 Area 103 Area

Claims (1)

A plurality of light sources emitting light of different hues, and a pixel portion;
The plurality of light sources are provided below the pixel portion,
The pixel portion has a plurality of pixels arranged in a matrix,
Each of the plurality of pixels has a light-transmitting first pixel electrode, a second pixel electrode that is disposed adjacent to the first pixel electrode, has reflectivity, a first transistor, and a second transistor. A transistor, and
The first pixel electrode is electrically connected to one of a source and a drain of the first transistor;
The other of the source and the drain of the first transistor is electrically connected to the first signal line;
A gate of the first transistor is electrically connected to a first scan line;
The second pixel electrode is electrically connected to one of a source and a drain of the second transistor;
The other of the source and the drain of the second transistor is electrically connected to the second signal line;
A gate of the second transistor is electrically connected to a second scan line;
In the pixel portion, the first scanning line and the second scanning line are provided in parallel,
In the pixel portion, the first signal line and the second signal line are provided in parallel,
A plurality of regions in which the first transistor is turned on to input a first image signal to the first pixel electrode, and the pixel portion includes a plurality of pixels in the scanning direction of the first scanning line. The color display is performed in a field sequential manner by selecting turning on or off the plurality of light sources for each of the plurality of regions.
A liquid crystal display device that turns off the plurality of light sources in a period in which the second transistor is turned on to input a second image signal to the second pixel electrode and display a still image;
A channel of the first transistor is formed in the first oxide semiconductor layer;
A channel of the second transistor is formed in a second oxide semiconductor layer;
In each of the plurality of pixels, the first oxide semiconductor layer is provided so as to overlap with the second pixel electrode of an adjacent pixel,
In each of the plurality of pixels, the second oxide semiconductor layer is provided so as to overlap with the second pixel electrode.

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